View source for Radar picket

{{Short description|Station used to increase radar detection range}}
[[File:Point Lay Alaska DEW Line.jpg|thumb|[[Point Lay, Alaska#Military radar|Former radar station at Point Lay, Alaska]].]]
[[File:USS Triton SSRN-586 Anaconda ad.JPG|thumb|[[USS Triton (SSRN-586)|USS ''Triton'' (SSRN-586)]]]]
[[File:E-1B VAW-121 CVW-6 CVA-42.jpg|thumb|[[E-1 Tracer|Grumman E-1 Tracer]]]]
A '''radar picket''' is a [[radar]]-equipped station, ship, submarine, aircraft, or vehicle used to increase the radar detection range around a nation or military (including naval) force to protect it from surprise attack, typically air attack, or from criminal activities such as [[smuggling]]. By definition a radar picket must be some distance removed from the anticipated targets to be capable of providing ''early warning''. Often several detached radar units would be placed in a ''ring'' to encircle a target to provide increased cover in all directions; another approach is to position units to form a ''barrier line''.

Radar picket units may also be equipped to direct friendly aircraft to intercept any possible enemy. In British terminology the radar picket function is called '''aircraft direction'''. A ship performing this function is termed a '''fighter direction ship'''. Airborne radar pickets are referred to as [[#Airborne early warning and control systems|Airborne early warning and control (AEW&C)]] or simply airborne early warning (AEW), depending on capabilities. 
{{See also|#Airborne early warning and control systems}}

In a sense radars intended to track [[ballistic missile]]s can be thought of as radar pickets (the early US [[Ballistic Missile Early Warning System|Ballistic Missile Early Warning System - BMEWS]] was originally termed as such), but because such systems also came to be used for tracking orbital [[satellites]] and [[space debris]] the current preferred term for them is [[Space domain awareness|space domain awareness systems]].

==World War II==
{{see|Radar in World War II}}
===United Kingdom World War II radar pickets===
====UK coastal radar====
[[Chain Home]] or CH was the codename for the ring of coastal early warning radar stations built by the [[Royal Air Force]] (RAF) before and during [[World War II]] to detect and track aircraft. Chain Home proved decisive during the [[Battle of Britain]] in 1940. The Chain Home network was continually expanded, with over 40 stations operational by the war's end. CH was not able to detect aircraft at low altitude, and from 1939 was normally partnered with the [[Chain Home Low]] system which could detect aircraft flying at any altitude over {{convert|500|ft|abbr=on}}. Ports were covered by Chain Home Extra Low, which gave cover down to {{convert|50|ft|abbr=on}} but at shorter ranges of approximately {{convert|30|mi|sigfig=1|abbr=out}}. In 1942 the [[AMES Type 7]] radar began to assume the job of tracking of targets once detected, and CH moved entirely to the early warning role.<ref>{{cite web |title=The prototype CH system – 1939… Chain, Home… Operational |url=http://histru.bournemouth.ac.uk/Oral_History/Talking_About_Technology/radar_research/chain_home_operational.html |date=1995–2009 |publisher=Bournemouth University |access-date=23 August 2009}}</ref>

====UK World War II AEW&C====
In late 1944 the [[Fighter Interception Development Unit RAF|Fighter Interception Development Squadron]] carried out operational trials under Operation Vapour of a [[Vickers Wellington#Airborne radar|Vickers Wellington]] which was equipped with a modified ASV Mk VI radar set and PPI, as one of the first Airborne Early Warning and Control (AEW&C) aircraft.<ref>{{cite book |title=Britain's Greatest Aircraft |last=Jackson |first=Robert |year=2007 |publisher=Pen & Sword Books Ltd. |location=Barnsley |isbn=978-1-84415-383-1 |pages=217 }}</ref> It operated at an altitude of 4,000 feet over the North Sea to control [[de Havilland Mosquito]] and [[Bristol Beaufighter]] [[night fighter]]s intercepting [[Heinkel He 111]] bombers flying from Dutch airbases and their [[V-1 flying bomb|V-1]] flying bombs. The Wellington was fitted with a homing beacon so the night fighters could locate and keep station with it. Despite encouraging results, the operational trials ended after the ''[[Luftwaffe]]'' stopped air launches by mid January 1945.

===German World War II radar pickets===
====Kammhuber Line====
[[Image:Kammhuber Line Map - Agent Tegal.png|thumb|right|A map of part of the Kammhuber Line stolen by a [[Belgium|Belgian]] agent and passed-on to the British in 1942. The 'belt' and [[nightfighter]] 'boxes' are shown ]]
The [[Kammhuber Line]] was the Allied name given to the German night air defense system established in July 1940 by Colonel [[Josef Kammhuber]]. The first version of the Line consisted of a series of 'boxes' of radar stations with overlapping coverage, layered three deep from Denmark to the middle of France, each covering a zone about 32&nbsp;km long (north-south) and 20&nbsp;km wide (east-west). Each station consisted of a control center with a [[Freya radar|FuMG A1 ''Freya'' radar]] with a range of about 100&nbsp;km and a directed searchlight for the night fighters. Later versions of the Line added two [[Würzburg radar|''Würzburg-Riese'' radars]], with a range of about 30&nbsp;km. Unlike the early-warning Freya, Würzburgs were accurate (and complex) tracking radars. One Würzburg would lock onto the target as soon as the Freya picked it up, and the second Würzburg would lock onto the night fighter as soon as it entered the box, thereby allowing controllers to get continual readings of the positions of both planes.{{sfn|Bowman|2016|p=144}}

The Line was very effective against early RAF Bomber Command tactics. However, on the night of 30/31 May 1942 in its 1,000 plane raid against Cologne, Bomber Command introduced the use of the [[bomber stream]]. The concentration of bombers through a few of the boxes resulted in the defenses being overwhelmed. In response, the Germans converted their ground radar into a radar network, which would follow the path of the British bombers, while a controller directed the night fighters into the stream. Measure and counter measure continued until October 1944, when German defenses were no longer able to respond to Germany's deteriorating situation.{{sfn|Bowman|2016|p=144}}

====''Kriegsmarine''====
From 1943 [[Nazi Germany]]'s ''[[Kriegsmarine]]'' operated several radar-equipped night fighter guide ships (''Nachtjagdleitschiffe''), including the [[German night fighter direction vessel Togo|NJL ''Togo'']]. which was equipped with a ''Freya'' radar for early warning and a ''Würzburg-Riese'' gun laying radar, plus night fighter communications equipment. From October 1943, ''Togo'' cruised the [[Baltic Sea]] under the operational control of the ''Luftwaffe''. In March 1944, after the [[Bombing of Helsinki in World War II#The great raids of February 1944|three great Soviet bombing raids on Helsinki]], she arrived in the [[Gulf of Finland]] to provide night fighter cover for [[Tallinn]] and [[Helsinki]].

===Japanese World War II radar pickets===
The [[Imperial Japanese Navy]] briefly modified two {{sclass|Ha-101|submarine|0}} submarines ({{ship|Japanese submarine|Ha-103||2}} and {{ship|Japanese submarine|Ha-105||2}}) as dedicated radar pickets in the first half of 1945, but reconverted them to an even more important role as tanker submarines in June of that year.

===United States World War II radar pickets===
====US Navy====
{{see also|#Replacement by aircraft}}
Radar picket ships first came into being in the [[US Navy]] during World War II to aid in the [[Allies of World War II|Allied]] advance to [[Japan]]. The number of radar pickets was increased significantly after the first major employment of [[kamikaze]] aircraft by the Japanese in the [[Battle of Leyte Gulf]] in October 1944. {{sclass|Fletcher|destroyer|0}} and {{sclass|Allen M. Sumner|destroyer|0}} [[destroyer]]s with SGA and [[SC radar]]s were pressed into picket service with few modifications at first – the ''Allen M. Sumner''s were the first destroyers to be designed with a [[combat information center]] (CIC), which made them ideal for this use.<ref>Friedman, Destroyers, pp. 126, 176</ref> Later, additional radars and fighter direction equipment were fitted, along with more light [[anti-aircraft]] (AA) guns for self-defense, usually sacrificing [[torpedo tube]]s to make room for the new equipment, particularly the large SP [[height-finding radar]]s of the era. Deploying some distance from the force to be protected along likely directions of attack, radar pickets were the nearest ships to the Japanese airfields. Thus, they were usually the first vessels seen by incoming waves of kamikazes, and were often heavily attacked.<ref>Friedman, Destroyers, pp. 202–206</ref>

[[File:USS Goodrich (DDR-831) underway c1958.jpeg|thumb|[[USS Goodrich (DD-831)|USS ''Goodrich'' (DDR-831)]] underway in 1950s radar picket configuration.]]

The radar picket system saw its ultimate development in World War II in the [[Battle of Okinawa]]. A ring of 15 radar picket stations was established around Okinawa to cover all possible approaches to the island and the attacking fleet. Initially, a typical picket station had one or two destroyers supported by two landing ships, usually [[Landing Craft Support|landing craft support (large) (LCS(L))]] or [[Landing Ship Medium|landing ship medium (rocket) (LSM(R))]], for additional AA firepower. Eventually, the number of destroyers and supporting ships were doubled at the most threatened stations, and [[combat air patrol]]s were provided as well. In early 1945, 26 new construction {{sclass|Gearing|destroyer|1}}s were ordered as radar pickets without torpedo tubes, to allow for extra radar and AA equipment, but only some of these were ready in time to serve off Okinawa. Seven [[destroyer escort]]s were also completed as radar pickets.
{{see also|#Destroyer escort conversions}}

The radar picket mission was vital, but it was also costly to the ships performing it. Out of 101 destroyers assigned to radar picket stations, 10 were sunk and 32 were damaged by kamikaze attacks. The 88 LCS(L)s assigned to picket stations had two sunk and 11 damaged by kamikazes, while the 11 LSM(R)s had three sunk and two damaged.<ref>Friedman, Destroyers, pp. 202–210, 230–233</ref><ref>[http://www.kamikazeimages.net/books/general/rielly/index.htm Review by William Gordon of Rielly, Robin L. "Kamikazes, Corsairs, and Picket Ships: Okinawa, 1945", Casemate Publishing, 2008] {{ISBN|1-93203-386-6}}.</ref>

The high casualties off Okinawa gave rise to the radar picket submarine, which had the option of diving when under attack. It was planned to employ converted radar picket submarines should the [[Operation Downfall|invasion of Japan]] become necessary. Two submarines ({{USS|Grouper||2}} and {{USS|Finback|SS-230|2}}) received rudimentary conversions during the war with the new SR search radars and the SV search radars mounted vertically as height finders,<ref name="Friedman, Submarines, pp. 90">Friedman, Submarines, pp. 90</ref> and two others ({{USS|Threadfin|SS-410|2}} and {{USS|Remora||2}}) were completed immediately after the war with the same suite, but none were used postwar in this role.<ref>Friedman, Submarines, pp. 253</ref>
{{see also|#Converted and purpose-built submarines}}

==Cold War==
{{see|Cold War}}
===United States and Canada===
[[File:Dew line 1960.jpg|thumb|A rough map of the three warning lines. From north to south: the DEW Line, Mid-Canada Line, and Pinetree Line. Off the coasts are the aircraft and ships representing the ocean barrier lines, and a 'Texas Tower'.]]
During the [[Cold War]], the [[Royal Canadian Air Force]] and the [[United States Air Force]] jointly built and operated radar picket stations to detect [[Soviet Union|Soviet]] bombers, and the United States Navy expanded the naval radar picket concept. The wartime radar picket destroyers (DDR) were retained, and additional DDRs, destroyer escorts (DER), submarines (SSR, SSRN), and auxiliaries (AGR) were converted and built in the years 1946–1959. The naval concepts were: 1) every carrier group would have radar pickets deployed around it for early warning of the increasing threat of Soviet [[air-to-surface missile]] attack, and 2) radar pickets would form barriers off the North American coasts, thus extending the land based lines. While on station, all of these assets – other than those assigned to fleet defense – were operationally controlled by the [[Aerospace Defense Command]] and after May 1958 [[North American Aerospace Defense Command|NORAD]].

====Fixed installations====
[[Image:Texas Tower 3.jpg|thumb|right|[[Texas Tower 3]]]]
During the 1950s the governments of [[Canada]], [[Denmark]], and the [[United States]] built three lines of fixed radar picket sites across Canada, and with the DEW Line into [[Alaska]] and [[Greenland]]. These were the [[Pinetree Line]] (1951), the [[Mid-Canada Line]] (1956), and the [[Distant Early Warning Line|Distant Early Warning (DEW) Line]] (1957). The DEW Line would be equipped with [[AN/FPS-19]], and until 1965 [[AN/FPS-23]] radars. There was also a line of radar sites in Alaska extending westward from the end of the DEW Line to the end of the [[Aleutian Islands]], and a line eastward from the Greenland end of the DEW Line to [[Iceland]], the [[Faroe Islands]], and [[Scotland]].

There were also three oil-rig-type offshore radar stations known as "[[Texas Towers]]" off the [[New England]] coast with [[AN/FPS-3]] (later AN/FPS-20) and [[AN/FPS-6]] radars.

While not designed as pickets ''per se'', coastal and interior fixed radars such as the interim [[Lashup Radar Network]] (1949), the [[Permanent System radar stations|Permanent System]] (1951), and [[SAGE radar stations|Semi-Automatic Ground Environment (SAGE)]] (1958), would function as pickets for areas removed from suspected airborne attackers.

====Command cruiser ''Northampton''====
[[File:USS Northampton (CLC-1) underway c1959.jpg|thumb|USS ''Northampton'' (CLC-1)]]
When the first [[supercarrier]] {{USS|United States|CVA-58|2}} was being designed in 1946, it was thought she would not be able to have an island or masts for radar or other antennas. Therefore, it was decided that a [[command ship]] was needed to escort the carrier and act not only in part as a radar picket (although from the center of the [[task force]] rather than the periphery as a true picket would), but also as the radar director of aircraft approach and landing on the carrier. The unfinished [[heavy cruiser]] {{USS|Northampton|CLC-1|2}} was converted under project [[Ship Characteristics Board|SCB 13]] into a command cruiser for this and other fleet command roles, with [[AN/SPS-2]] (one of only two ships with this huge installation), AN/SPS-3, and [[AN/SPS-8]] radars. The subsequent invention of the [[angled flight deck]] made it possible to install islands and radar on supercarriers, and so this role was eliminated from the ''Northampton'' conversion.<ref>Freidman, Cruisers pp. 340</ref>

====Converted and purpose-built submarines====
The U.S. Navy continued to develop radar picket submarines (SSRs) after World War II under Project Migraine, and by 1953, a total of 10 new SSR conversions had been performed with SR-2 and SV-2 radars:
* Migraine I: in 1946 submarine radar picket conversions were performed on {{USS|Spinax|SS-489|2}} and [[USS Requin (SS-481)#Radar picket operations|''Requin'']]; these were more extensive than the rudimentary conversions made a year earlier for the planned invasion of Japan. The radar equipment of these diesel submarines took the place of torpedoes in the stern torpedo rooms. The radar antennas were mounted directly on the hull above the equipment, where they suffered spray damage.<ref name="Friedman, Submarines, pp. 90"/>
* Migraine II (aka project [[Ship Characteristics Board|SCB 12]]) involved raising the antennas off the hull onto masts, moving the equipment to the aft battery room (higher capacity [[Greater Underwater Propulsion Power Program|GUPPY]] batteries were installed forward to compensate), and adding topside fathometers to give a limited under-ice capability. The aft torpedo tubes were removed and the compartment used for berthing and storage. {{USS|Burrfish||2}} and [[USS Tigrone (SS-419)#Post-War Activities|''Tigrone'']] were converted, and the two Migraine I submarines were also upgraded to this standard.<ref>Friedman, Submarines, pp. 91–93</ref> 
{{further|Balao-class submarine#Radar picket}}
{{further|Tench-class submarine#Radar picket}}
* Migraine III (aka SCB 12A) had the most extensive conversion with an added {{convert|27.5|ft|m|adj=on}} compartment for an expanded CIC. The search antenna was moved to an enlarged sail located over the new compartment. Converted were ''[[USS Pompon#Post-war service as radar picket|Pompon]]'', ''[[USS Rasher#Service as radar picket submarine, 1953–1960|Rasher]]'', ''[[USS Raton#Radar picket submarine (SSR-270), 1953–1959|Raton]]'', ''[[USS Ray (SS-271)#Radar picket submarine (SSR-271), 1952–1958|Ray]]'', ''[[USS Redfin#Radar picket submarine, 1953–1959|Redfin]]'', and ''[[USS Rock#Radar picket submarine (SSR-274), 1953–1959|Rock]]''.<ref>Friedman, Submarines, pp. 91–94, 96–97</ref>
{{further|Gato-class submarine#Radar picket}}
In 1956 two large, purpose-built diesel SSRs, the {{sclass|Sailfish|submarine|4}}, were commissioned. These were designed under project SCB 84 for a high surface speed with the intent of scouting in advance of carrier groups, and were equipped with large BPS-2 and BPS-3 radars. However, the SSRs did not fare well in this mission. Their maximum surfaced speed of 21 knots was too slow to effectively operate with a carrier group, although it was sufficient for amphibious group operations.<ref>Friedman, Submarines, pp. 94–95</ref>

It was thought that nuclear power would solve this problem. The largest, most capable, and most expensive radar picket submarine was the nuclear-powered {{USS|Triton|SSRN-586}}, designed under project SCB 132 and commissioned in 1959 with the AN/SPS-26 radar (an electronically scanned radar fully adapted for submarine use and intended for ''Triton'', BPS-10, was never completed). The longest submarine built by the United States until the {{sclass|Ohio|submarine|4}} [[Trident missile]] submarines of the 1980s, ''Triton'''s two reactors - the only US submarine so powered - allowed her to exceed 30 knots on the surface.<ref>Friedman, Submarines, pp. 94–98</ref><ref name=whitman>{{cite web|last=Whitman|first=Edward C.|title=Cold War Curiosities: U.S. Radar Picket Submarines|url=http://www.navy.mil/navydata/cno/n87/usw/issue_14/coldwar.html|publisher=Undersea Warfare|access-date=26 January 2014|date=Winter–Spring 2002|archive-date=10 October 2012|archive-url=https://web.archive.org/web/20121010150930/http://www.navy.mil/navydata/cno/n87/usw/issue_14/coldwar.html|url-status=dead}}, Issue 14</ref>

====List of radar picket submarines<ref name=whitman/>====
[[File:SSR-419 Tigrone.gif|thumb|left|Atlantic Fleet’s {{USS|Tigrone|SS-419|2}} in ''Migraine II'' radar picket configuration]]
[[File:USS Sailfish;0857203.jpg|thumb|right|Atlantic Fleet’s purpose-built {{USS|Sailfish|SSR-572|2}} with BPS-2 and BPS-3 installations]]
{{column
|1=
:[[US Atlantic Fleet]]
:*{{USS|Pompon|SSR-267}}
:*{{USS|Ray|SSR-271}}
:*{{USS|Redfin|SSR-272}}
:*{{USS|Burrfish|SSR-312}}
:*{{USS|Tigrone|SSR-419}}
:*{{USS|Requin|SSR-481}}
:*{{USS|Sailfish|SSR-572}}
:*{{USS|Triton|SSRN-586}}
}}
[[Image:USS Raton;0827015.jpg|thumb|left|Pacific Fleet’s {{USS|Raton|SSR-270|2}} in ''Migraine III'' configuration]]
{{column
|1=
:[[US Pacific Fleet]]
:*{{USS|Rasher|SSR-269}}
:*{{USS|Raton|SSR-270}}
:*{{USS|Rock|SSR-274}}
:*{{USS|Spinax|SSR-489}}
:*{{USS|Salmon|SSR-573}}
}}

====Destroyer escort conversions====
[[File:Lockheed WV-2 of VW-15 flies over USS Sellstrom (DER-255) off Newfoundland, in March 1957.jpg|thumb|An Atlantic barrier [[EC-121 Warning Star|Lockheed WV-2 Warning Star]] (later EC-121) and the radar picket destroyer escort {{USS|Sellstrom|DER-255}} off Newfoundland in 1957.]]
The 26 wartime ''Gearing''-class DDRs were supplemented by nine additional conversions during the early 1950s. The seven wartime DERs were not considered worth modernizing and were relegated to secondary roles, so 36 additional DER conversions were performed in 1951 through 1958:

*Six diesel-powered {{sclass|Edsall|destroyer escort|0}} DEs were converted into DERs in 1951 and 1952 under project [[Ship Characteristics Board|SCB 46]]: converted were ''[[USS Fessenden (DE-142)#Converted to Radar Picket Ship|Fessenden]]'', ''[[USS Harveson (DE-316)#Conversion to radar picket ship|Harveson]]'', ''[[USS Joyce (DE-317)#Converted to Radar Picket Ship|Joyce]]'', ''[[USS Kirkpatrick (DE-318)#Converted to Radar Picket Ship|Kirkpatrick]]'', ''[[USS Otterstetter (DE-244)#Post-War Conversion to Radar Picket Ship|Otterstetter]]'', and [[USS Strickland (DE-333)#Cold War|''Strickland'']].<ref>Friedman, Destroyers, pp 230–231</ref>
*Two DEs which were unfinished at the end of World War II, {{USS|Vandivier||2}} and [[USS Wagner#Conversion to radar picket ship|''Wagner'']], were completed as DERs in 1954 under SCB 46A. As {{sclass|John C. Butler|destroyer escort|0}} DEs they had steam powerplants and so lacked the endurance of their diesel half sisters. This was an experiment intended to validate the conversion should the design be required for any future mobilization. These two ships would be the first DERs to be retired, in 1960.<ref>Friedman, Destroyers, pp 231–232</ref>
*Another 28 ''Edsall''-class DEs would be converted into DERs from 1954 through 1957 under SCB 46B.<ref>Friedman, Destroyers, p 232</ref>

The DERs were used in 1955–1965 to form two Barrier Forces known as BarLant and BarPac, which extended the DEW Line from [[Argentia Naval Base|Argentia]], [[Newfoundland]] to the [[Lajes Field|Azores]] in the Atlantic, and from [[Adak Naval Air Station|Adak, Alaska]] to [[Midway Atoll|Midway]] in the Pacific.<ref name="Friedman, Destroyers, pp. 231–233">Friedman, Destroyers, pp. 231–233</ref>

====Converted merchant ships====
[[Image:USS Tracer (AGR-15).jpg|thumb|[[USS Tracer (AGR-15)|USS ''Tracer'' (AGR-15)]], an ocean radar picket ship]]
{{main|Guardian-class radar picket ship}}

From 1955 to 1965 the [[United States Navy]] employed ''Guardian'' class radar picket ships (converted under project SCB 126 from the former boxed aircraft transport version of the [[Liberty ship]]) to create barrier lines off the East and West Coasts. They were equipped with AN/SPS-8 (later [[AN/SPS-30]] on some ships), [[AN/SPS-6#AN/SPS-12|AN/SPS-12]], and AN/SPS-17 radars (the last was specially designed for these ships). Eight were homeported at [[Treasure Island, San Francisco|Treasure Island, California]] and eight at [[Davisville, Rhode Island]]. The [[hull classification symbol]] of the ships was initially YAGR, changed to AGR in 1958 (this change moved the ships from the [[List of yard and district craft of the United States Navy#Radar picket ships (YAGR)|naval yard and district craft]] category to the [[List of auxiliaries of the United States Navy#Radar picket ships (AGR)|naval auxiliary]] category). The standard crew consisted of 13 officers, 8 chief petty officers, and 125 enlisted.<ref>[http://www.yagrs.org/ships.htm YAGR Website Ship List]</ref>

Picket stations were about {{convert|400|–|500|mi}} off each coast and provided an overlapping radar or electronic barrier against approaching aircraft. Typical station duty was about 30–45 days out and 15 days in port. While on station, each ship stayed within a specific radius of its assigned picket station, reporting and tracking all aircraft contacts. Each ship carried qualified air controllers to direct intercept aircraft sent out to engage contacts. While on station additional duties such as search and rescue, weather reporting, fishery studies, and other miscellaneous duties were assigned.

====Replacement by aircraft====
[[File:TBM-3W at NAS Patuxent River c1946.jpg|thumb|Grumman TBM-3W Avenger]]
[[File:Boeing PB-1W in flight.jpg|thumb|right|Boeing PB-1W]]
[[File:HR2S-1W NAN3-57 1-57.jpg|thumb|Sikorsky HR2S-1W early warning helicopter]]
The U.S. Navy began to develop airborne early warning (AEW) aircraft in the last years of World War II under [[AN/APS-20#Design and development|Project Cadillac]]. The first U.S. AEW aircraft were the 1945 carrier based [[Grumman TBF Avenger|Grumman TBM-3W Avenger]] under Project Cadillac I, followed by the 1948 [[Douglas A-1 Skyraider#Variants|Douglas AD-3W, −4W, and −5W Skyraider]] and the 1950 [[Grumman AF Guardian|Grumman AF-2W Guardian]] (not to be confused with the AGR ships of the same name); though the Skyraiders and Guardians were built in large numbers, none were very successful as they were too small to function as a full CIC, and all were used more often in the [[anti-submarine warfare]] (ASW) role. All of these aircraft used the [[AN/APS-20]] radar. While the 1957 carrier-compatible [[Sikorsky CH-37 Mojave#Variants|Sikorsky HR2S-1W helicopter]] with the AN/APS-20E or AN/APS-32 radar (sources differ) had room for a full CIC it also failed, largely due to excessive vibration, slow speed, and cost.<ref name="sikarchs-56">{{cite web |title=S-56/HR2S-1/H-37 Helicopter |url=https://www.sikorskyarchives.com/S+56%20HR2S-1H-37.php |website=sikorskyarchives |access-date=26 May 2019}}</ref>

Another 1945 development was the land based [[List of Boeing B-17 Flying Fortress variants#PB-1 and PB-1W|Boeing PB-1W]], a naval B-17 variant modified under Project Cadillac II to carry the AN/APS-20 radar and a full CIC; this aircraft entered service too late for combat but was used for further development of the AEW concept.<ref name=USNI_202303>{{cite web |title=A Bomber Without Bombs |url=https://www.usni.org/magazines/naval-history-magazine/2023/april/bomber-without-bombs |first=Norman |last=Polmar |work=Naval History Magazine |access-date=21 March 2023 |date=April 2023}}</ref>

Far more successful was the land based [[Lockheed EC-121 Warning Star]], which was introduced in 1954 in both Air Force and Navy service as pickets and in other roles with the AN/APS-20 and AN/APS-45 radars, respectively under and atop the aircraft. As pickets the Air Force EC-121s provided radar coverage by flying "Contiguous Barrier" orbits 300 miles offshore, between the coasts and the AGR Guardian picket lines. The Navy version (designated PO-1W, then WV-1, −2, and −3 [[1962 United States Tri-Service aircraft designation system|before 1962]]) flew over the more distant BarLant and BarPac DER lines. They would later be re-equipped with AN/APS-95 and AN/APS-103 radars. Their main deficiency was lack of endurance, which made them unsuitable for naval fleet coverage.

[[File:ZPG-3W blimp US Navy 1960.jpg|thumb|Goodyear ZPG-3W]]
Perhaps the most successful airborne radar pickets were the nine [[N-class blimp|Goodyear ZPG-2W and ZPG-3W blimps]]: the −2W blimps were equipped with the AN/APS-20 and AN/APS-69 radars in an arrangement similar to the EC-121s, while the −3W blimps (the largest ever built) had the large AN/APS-70 radar placed inside their gas envelopes. Starting in 1955 they successfully combined airborne early warning radar surveillance and long endurance in all possible roles, but they were fragile, too slow to quickly reach stations far from base, and expensive (their overhead costs also increased after the ASW blimps were retired, having become technically obsolete due to the introduction of higher performance nuclear submarines). They were retired in 1962.<ref>Sky Ships: A History of the Airship in the United States Navy, Althoff, W.F., Pacifica Press, c1991, {{ISBN|0-935553-32-0}}</ref>

[[File:Grumman E-2A Hawkeye in flight in the early 1960s.jpg|thumb|right|Grumman E-2A Hawkeye]]
The introduction of the [[E-1 Tracer|Grumman WF-2 Tracer]] (later the E-1 Tracer) carrier-based airborne early warning aircraft in 1958 with the AN/APS-82 radar followed by the [[Northrop Grumman E-2 Hawkeye|Grumman E-2 Hawkeye]] with the AN/APS-120 radar in 1964 doomed the surface and submarine radar pickets as carrier escorts (later E-2 models would see the APS-120 replaced in succession with the APS-125, −139, −145, and AN/APY-9 radar). Airborne radar had now evolved to the point where it could warn of an incoming attack more efficiently than a surface ship. In 1961 the DDRs and SSRs were withdrawn. All but six DDRs received ASW conversions under the [[FRAM I]] and FRAM II programs and were redesignated as DDs; the remaining six were somewhat modernized under FRAM II and retained in the DDR role. The SSRs were converted to other roles (the ''Sailfish'' class was converted to an [[attack submarine]] design under project SCB 242), or scrapped. ''Triton'' was left without a mission. She was too large to function as an attack submarine; some alternatives were considered, including serving as an [[National Emergency Command Post Afloat|underwater national command post]], but she eventually became the first US nuclear submarine to be decommissioned, in 1969.<ref name="Friedman, Destroyers, pp. 231–233"/><ref>Friedman, Submarines, pp. 96, 98</ref><ref name=whitman/>

====Replacement by OTH radar====
By 1965, the development of [[over-the-horizon radar]] (OTH) made the barrier forces obsolete, and the DERs and the AGR Guardians were retired. The EC-121s would be allocated to other roles. OTH radar also played a small part in the retirement of the obsolete Pinetree Line, Mid-Canada Line, and the AN/FPS-23 radars of the DEW Line.

====PIRAZ during Vietnam====
The final use of the radar picket concept by the US Navy was in the [[Vietnam War]]. The [[Gulf of Tonkin]] Positive Identification Radar Advisory Zone ([[PIRAZ]]) guided missile [[List of cruisers of the United States Navy#Guided missile cruisers (CAG, CLG, CG)|cruisers]] (and [[destroyer leader]]s aka [[frigate]]s which would later be [[United States Navy 1975 ship reclassification|redesignated]] as cruisers in 1975) provided significant air control and air defense in that war.<ref>Friedman, Destroyers, p. 227</ref>

===United Kingdom===
====British coastal radar====
In the 1950s the Chain Home sites were either retired or converted into the [[ROTOR]] network, and then into the [[Linesman/Mediator]] network starting in the mid-1960s.
====British aircraft direction ships====
[[Image:Battleaxe2.jpg|thumb|{{HMS|Battleaxe|D118}}, a {{sclass2|Weapon|destroyer|1}}, after aircraft direction conversion]]
[[Image:HMS Lincoln. 1972.jpg|thumb|{{HMS|Lincoln|F99}}, a {{sclass|Salisbury|frigate|1}}, in 1972]]
The British [[Royal Navy]] constructed or converted two types of dedicated aircraft direction ships in the late 1950s and early 1960s. Four [[World War II]] [[Battle-class destroyer#Aircraft Direction Conversion|Battle-class destroyers]] and four [[Weapon-class destroyer#Modification|Weapon-class destroyers]] were converted 1959–1962 as Fast Air Detection Escorts to accompany fast carrier groups. Also, four Type 61 {{sclass|Salisbury|frigate|1}}s were commissioned 1957–1960 to accompany slow carrier or amphibious groups. However, the aircraft direction function was short-lived. With the mid-1960s decision to phase out the fast carriers, the ''Battle''-class ships were placed in reserve 1966–1968 and were scrapped or converted to non-combat roles by 1974. The ''Salisbury'' class were relegated to non-combat roles or sold by the end of 1978.

====British AEW====
The Royal Navy began to operate the AEW version of the Douglas Skyraider in 1951. A more capable aircraft was desired, and the [[Fairey Gannet AEW.3]] was the winner of a competition to replace the Skyraiders. Using the same AN/APS-20 radar as the Skyraiders, the Gannets entered service in 1960 and remained until the last full deck carrier was retired in 1978.<ref name="Gibson10">{{harvnb|Gibson|2011}}</ref>

In anticipation of the retirement of the Gannets, in 1972 the RAF converted 12 [[Avro Shackleton]] maritime patrol aircraft to an AEW configuration by adding the AN/APS-20 radar to the underside of the aircraft; the last of these were retired in 1991.<ref name="Tyack 87">Tyack 2005, p. 87.</ref>

===Soviet Union===
====Soviet radar picket ships====
[[Image:ORP Dzik projektu 254M.jpg|thumb|right|ORP ''Dzik'', a [[Polish Navy]] T-43 class minesweeper (official image caption reads 'projektu 254M' but the aft turret has not been removed for the radar)]]
Twenty {{sclass2|T43|minesweeper|1}}s were converted to [[List of ships of Russia by project number|Project 254]] KVN-50-class radar picket ships between 1955 and 1959. Modifications involved replacing the aft [[gun turret]] with a [[P-8 radar|Pegmantit 8]] ([[NATO reporting name]]: "Knife Rest-A") or [[MP-500 radar]] (NATO: "Big Net") radar. Most were retired during the 1970s or relegated to training duties, with the last withdrawn in 1987.<ref name="JWS">{{cite book|title=Jane's Weapon Systems 1988– 1989|page=618|publisher=Jane's Information Group|year=1987|isbn=9780710608550}}</ref>

Fourteen further T43-class minesweepers were converted to Project 258 KVN-6-class radar picket ships between 1973 and 1977 with ''[[MR-200 radar|Kaktus]]'' radars. Some were later modified to Project 258M ships with ''[[MR-302 radar|Rubka]]'' (NATO: "Strut Curve") radars.<ref name="JWS"/>

Three {{sclass2|T58|minesweeper|1}}s were converted to radar picket ships between 1975 and 1977 by replacing the aft 57&nbsp;mm gun turret with a [[P-10 radar|Pegmantit 10]] (NATO: "Knife Rest-B") radar.<ref name="GSN"/>{{rp|198}}

Three other projects were cancelled before conversions were made.
* Project 959 – further conversions the T58-class minesweeper with upgraded radar
* Project 962 – a fourth cruiser type following on from the {{sclass2|Kresta I|cruiser|5}}, {{sclass2|Kresta II|cruiser|5}} and {{sclass2|Kara|cruiser|5}} designs<ref>{{cite book|title=Soviet Cold War Guided Missile Cruisers|page=51|author=Edward Hampshire|publisher=Bloomsbury Publishing|year=2017|isbn=978-1472817426}}</ref>
* Project 996 - conversion of a {{sclass|Sovremennyy|destroyer|2}}

====Soviet radar picket submarines====
Four [[Whiskey-class submarine|Project 640 submarines]] were converted as radar picket boats between 1959 and 1963 by fitting Project 613 submarines with "Boat Sail" radar in an enlarged conning tower. These were known to NATO as "Whiskey Canvas Bag" submarines from the canvas coverings often put over the radar when NATO aircraft approached. While the US radar picket submarines were intended for fleet defense, the Project 640 boats were intended to provide warning of air attacks on Soviet coastal territory.<ref>{{cite book|title=Cold War Submarines: The Design and Construction of U.S. and Soviet Submarines|page=27|author=[[Norman Polmar]] and Kenneth J. Moore|publisher=Potomac Books|year=2004|isbn=1574885944}}</ref><ref name="GSN">{{cite book|title=Guide to the Soviet navy|author=Norman Polmar|publisher=Naval Institute Press|year=1983|isbn=0870212397}}</ref>{{rp|119}}

====Soviet AEW====
[[File:Tupolev Tu-126, Zokniai, Šiauliai, Lithuanian SSR.jpg|thumb|Tupolev Tu-126]]
In 1958 the Soviet Union began development of an aircraft intended to act as an airborne early warning (AEW) radar picket in the far north along the Arctic coast, so that the expense of land stations could be avoided. The result, the [[Tupolev Tu-126]] (NATO: "Moss"), entered service in 1965, but the ''Liana'' (NATO: "Flat Jack") radar was ineffective in tracking low flying targets over land, and suffered from reflections from the aircraft's propellers.<ref>Duffy and Kandalov, Tupolev, p136"</ref>

The [[Beriev A-50]] "Mainstay" replaced the Tu-126. It first flew in 1978.<ref>[https://spyflight.co.uk/aircraft/#Beriev  "Beriev A-50 Mainstay."] ''Spyflight.co.uk.'' Retrieved: 27 October 2011.</ref>

In 1979 the development of the [[Yakovlev Yak-44]] was begun; this aircraft would have performed the AEW role aboard later Soviet aircraft carriers. It was similar in layout to the Grumman E-2 Hawkeye, and it would have carried a [[Vega Radio Engineering Corporation|NPO Vega]] pulse-doppler radar in a rotodome. The project was cancelled in 1993.<ref name="OKB p347">Gordon, Komissarov and Komissarov 2005, p. 347.</ref>

==Late and post-Cold War==
===Post-1980 fixed installations===
In North America SAGE was replaced with the [[Joint Surveillance System]] in 1980-1983, and the DEW line was replaced with the [[North Warning System]] in 1988-1993.<ref name="SOW">{{cite web |title=North Warning System (NWS) Office Statement of Work |url=https://buyandsell.gc.ca/cds/public/2021/03/31/4e8d94dff0f4235b75242f90c7650954/sow_-_edt.zip |format=Compressed PDF file |website=Buyandsell.gc.ca |publisher=Public Services and Procurement Canada |access-date=6 June 2021 |archive-url=https://web.archive.org/web/20210606005827/https://buyandsell.gc.ca/cds/public/2021/03/31/4e8d94dff0f4235b75242f90c7650954/sow_-_edt.zip|archive-date=6 June 2021 |language=en, fr|date=November 2020|url-status=live}}</ref>.{{rp|16}} 

In Britain the Linesman/Mediator network would be replaced with the [[Improved United Kingdom Air Defence Ground Environment]] in the 1990s.{{sfn|Gough|1993}}

===Airborne early warning and control systems===
[[File:Royal Air Force (RAF) E-3D Sentry AEW1 (airborne early warning) aircraft, registration ZH106, taking part in Exercise Taurus Mountain 3, in the skies over North Yorkshire in March 2012 - MOD 45153803 (cropped).jpg|thumb|A [[Royal Air Force]] [[E-3 Sentry]] over [[North Yorkshire]].]]
{{main|Airborne early warning and control}}
Airborne early warning and control systems (AEW&C, aka AWACS in the U.S.) were developed to replace the AEW radar pickets of the 1960s. These aircraft have capabilities far beyond their predecessors. They can perform complex [[command and control]] of a [[battlespace]] in air engagements by directing fighter and attack aircraft strikes. AEW&C units are also used to carry out [[Aerial surveillance|surveillance]], including [[Airborne ground surveillance|over ground targets]] and frequently perform BMC2 ([[battle management]] command and control) functions. They are still capable of performing radar picket duties, though they are seldom used in this role.<ref>Neufeld 1997, p. 276.</ref>

China is developing the [[Xi'an KJ-600]] carrier borne AEW&C; first flight was on 29 August 2020.<ref>{{cite magazine |last=Suciu |first=Peter |date=5 September 2020 |title=The Xian KJ-600 Could Make China's Aircraft Carriers Far More Powerful |url=https://nationalinterest.org/blog/buzz/xian-kj-600-could-make-chinas-aircraft-carriers-far-more-powerful-168497 |magazine=[[The National Interest]] |access-date=9 September 2020}}</ref>

===Tethered aerostats===
[[File:MarfaTX.jpg|thumb|Tethered Aerostat Radar System]]
Beginning in 1980 the United States installed a barrier line of tethered [[aerostat]]s to detect low flying aircraft over Cuba and the U.S.-Mexican border, known as the [[Tethered Aerostat Radar System]].<ref>{{cite web | date = 2010-03-29 | title = Tethered Aerostat Radar System | url = http://www.af.mil/information/factsheets/factsheet.asp?id=3507 | url-status = dead | archive-url = https://web.archive.org/web/20100409224139/http://www.af.mil/information/factsheets/factsheet.asp?id=3507 | website = [[United States Air Force]] | archive-date = 2010-04-09 | access-date = 2023-12-19 | df = dmy-all}}</ref>

[[Israel]] developed a similar system, the [[EL/M-2083]], which it sold to [[India]] and [[Singapore]].<ref>{{Cite web |url=http://www.iai.co.il/Sip_Storage//FILES/6/41636.pdf |title=Aerostat Early Warning Radar - ELM-2083 |access-date= 2023-12-19 | archive-date = 2017-12-01 |archive-url=https://web.archive.org/web/20171201041346/http://www.iai.co.il/Sip_Storage//FILES/6/41636.pdf |url-status=dead | website = [[Israel Aerospace Industries]] | df = dmy-all }}</ref>

A similar system, [[JLENS]], was developed starting in 1998 by the United States for tracking [[cruise missile]]s and other threats, but was cancelled in 2017.<ref>{{cite news | first1 = Marcus | last1 = Weisgerber | date = 2015-12-05 | url = https://www.defenseone.com/technology/2015/12/jlens-supporters-never-mind-blimp-save-radar/124219/ | work = [[Government Executive|Defense One]] | title = JLENS Supporters: Never Mind the Blimp, Save the Radar | archive-url = https://web.archive.org/web/20231112112358/https://www.defenseone.com/technology/2015/12/jlens-supporters-never-mind-blimp-save-radar/124219/ | archive-date = 2023-11-12 | access-date = 2023-12-19 | url-status = live | df = dmy-all }}</ref>

===Long endurance unmanned aerial vehicles (UAVs)===
Proposals have been made to install similar radars on [[High-altitude platform station|long-endurance UAVs]], although there are conflicts between radar power requirements and UAV endurance.

==See also==
{{Portal|United Kingdom|Soviet Union}}
*[[Early-warning radar]]
*[[List of radars]]
*{{slink|List of auxiliaries of the United States Navy#Radar Picket Ships (AGR)}}
*{{slink|List of yard and district craft of the United States Navy#Radar Picket Ships (YAGR)}}
*[[Picket (military)]]
*[[Picket boat]]
*[[United States general surveillance radar stations]]

{{Commons category|Guardian class radar picket ships}}
{{Commons category|Battle class destroyer}}
{{Commons category|Salisbury class frigate}}

==References==
{{AFHRA}}

===Notes===
{{Reflist}}

===Sources===
{{Refbegin}}
* [http://www.history.navy.mil/research/library/online-reading-room/title-list-alphabetically/b/battle-experience-radar-pickets.html Battle Experience: Radar Pickets and Methods of Combating Suicide Attacks off Okinawa, 20 July 1945.]
* {{Cite book |last=Bowman |first=Martin |year=2016 |title=Nachtjagd, Defenders of the Reich 1940–1943 |location=Barnsley, South Yorkshire  |publisher=[[Pen and Sword Books]] |isbn=978-1-4738-4986-0}}
* [https://web.archive.org/web/20120921014430/http://www.dtic.mil/doctrine/dod_dictionary/data/r/6440.html dtic.mil definition of radar picket]
* Duffy, Paul and Kandalov, Andrei. ''Tupolev: The Man and His Aircraft''. Shrewsbury, UK: Airlife, 1996. {{ISBN|1-85310-728-X}}.
* {{cite book | last = Friedman | first = Norman | author-link = Norman Friedman | title = US Destroyers: An Illustrated Design History | publisher = Naval Institute Press | year = 2004 | location = Annapolis | isbn = 1-55750-442-3 | edition = Revised }}
* {{cite book |last=Friedman|first=Norman |title=U.S. Submarines Since 1945: An Illustrated Design History |publisher=[[United States Naval Institute]] |year=1994|location=[[Annapolis, Maryland]] |isbn=1-55750-260-9}}
* {{citation|last=Friedman|first=Norman|title=U.S. Cruisers: an illustrated design history|publisher=Naval Institute Press|location=Annapolis, MD|year=1984|isbn=0-87021-718-6|oclc=10949320}}
* {{cite book |last=Gibson |first=Chris |title=The Admiralty and AEW: Royal Navy Airborne Early Warning Projects |location=Tyne and Wear |publisher=Blue Envoy Press| year=2011 |isbn=978-095619-512-8}}
* {{Cite book |last1=Gordon |first1=Yefim |last2=Komissarov |first2=Dmitry |last3=Komissarov |first3=Sergey |title=OKB Yakovlev: A History of the Design Bureau and its Aircraft |publisher=Midland Publishing |location=Hinkley, UK |year=2005 |isbn=1-85780-203-9}}
* {{cite book
 |first=Jack |last=Gough
 |title=Watching the Skies: a history of ground radar for the air defence of the United Kingdom by the Royal Air Force from 1946 to 1975
 |publisher=HMSO
 |isbn=978-0-11-772723-6
 |date=1993
 |url=https://books.google.com/books?id=VHcfAQAAIAAJ
 }}
* {{Cite book |last1=Neufeld |first1=Jacob |last2=Watson Jr. |first2=George M. |last3=Chenoweth |first3=David |title=Technology and the Air Force. A Retrospective Assessment |publisher=United States Air Force |location=Washington, D.C. |year=1997 |pages=267–287}} http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA440094&Location=U2&doc=GetTRDoc.pdf {{Webarchive|url=https://web.archive.org/web/20121007221217/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA440094&Location=U2&doc=GetTRDoc.pdf |date=2012-10-07 }}
* [https://archive.today/20120709042319/http://guppysubmarinetribute.homestead.com/Tribute.html GUPPY, SSR, and other diesel boat conversions page]
* [https://web.archive.org/web/20050204013020/http://usspringle.org/rp14map.htm Map of Okinawa picket stations in April 1945]
* [http://www.kamikazeimages.net/books/general/rielly/index.htm Review by William Gordon of Rielly, Robin L. ''Kamikazes, Corsairs, and Picket Ships: Okinawa, 1945'', Casemate Publishing, 2008] {{ISBN|1-93203-386-6}}.
* Tyack, Bill "Maritime Patrol in the Piston Engine Era" ''Royal Air Force Historical Society Journal'' '''33''', 2005 {{issn|1361-4231}}
* [https://web.archive.org/web/20050225122325/http://ussdrexler.net/radar.html USS Drexeler description of protection of Okinawa]
* [http://www.navy.mil/navydata/cno/n87/usw/issue_14/coldwar.html Whitman, Edward C. "Cold War Curiosities: U.S. Radar Picket Submarines", ''Undersea Warfare'', Winter-Spring 2002, Issue 14] {{Webarchive|url=https://web.archive.org/web/20121010150930/http://www.navy.mil/navydata/cno/n87/usw/issue_14/coldwar.html |date=2012-10-10 }}
* [http://www.yagrs.org/ships.htm YAGR Website Ship List]
{{Refend}}

== External links ==
* [https://nuke.fas.org/guide/usa/airdef/art5-su9.htm Guarding the Cold War Ramparts: The U.S. Navy’s Role in Continental Air Defense, Federation of American Scientists, reprinted from the Naval War College Review, Summer 1999]

[[Category:Force protection tactics]]
[[Category:Naval warfare tactics]]
[[Category:Aerial warfare tactics]]
[[Category:Anti-aircraft warfare]]
[[Category:Ships by type]]
[[Category:Boats by type]]
[[Category:Radar picket ships by country]]