USS Mobjack (AGP-7)

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For other ships of the same name, see USC&GS Pioneer.
USS Mobjack (AGP-7)
USS Mobjack (AGP-7) off Houghton, Washington, on her commissioning day, 17 September 1943
Career (United States Navy)
Name: USS Mobjack (AVP-27)
Namesake: Mobjack Bay, on the western shore of Chesapeake Bay in Virginia
Builder: Lake Washington Shipyard, Houghton, Washington
Laid down: 25 February 1942
Launched: 2 August 1942
Sponsored by: Mrs. H. R. Peck
Reclassified: Motor torpedo boat tender (AGP-7) 11 March 1943
Commissioned: 17 October 1943
Decommissioned: 21 August 1946
Honors and
Three battle stars for her World War II service
Fate: Transferred to U.S. Department of Commerce 21 August 1946
Career (United States Coast and Geodetic Survey) Flag of the United States Coast and Geodetic Survey.svg
Name: USC&GS Pioneer (OSS 31)
Namesake: Pioneer, one who goes before, as into the wilderness, preparing the way for others to follow
Acquired: 21 August 1946
In service: 1946
Out of service: 1966
Fate: Sold for scrapping 4 May 1966
General characteristics (Seaplane tender)
Class & type: Barnegat-class seaplane tender, converted during construction into a motor torpedo boat tender
Displacement: 1,760 tons (light)
2,750 tons (full load)
Length: 310 ft 9 in (94.72 m)
Beam: 41 ft 1 in (12.52 m)
Draft: 13 ft 6 in (4.11 m)
Installed power: 6,000 horsepower (4.48 megawatts)
Propulsion: Four diesel engines, two shafts
Speed: 18.2 knots
Complement: 360
Sensors and
processing systems:
Radar; sonar
Armament: 2 x 5-inch (127-millimeter) guns
8 x 40-millimeter anti-aircraft guns
2 × depth charge tracks
General characteristics (Survey ship)
Type: Ocean survey ship
Length: 311.6 ft (95.0 m)
Beam: 41 ft (12 m)
Draft: 13.8 ft (4.2 m)

USS Mobjack (AVP-27/AGP-7) was a motor torpedo boat tender in commission in the United States Navy from 1943 to 1946 that saw service in the latter portion of World War II. From 1946 to 1966, she served in the United States Coast and Geodetic Survey as the survey ship USC&GS Pioneer (OSS 31), the third Coast and Geodetic Survey ship of the name.

Construction and commissioning[edit]

Mobjack was laid down as a seaplane tender, AVP‑27, by Lake Washington Shipyard, Houghton Washington, on 25 February 1942 and launched on 2 August 1942, sponsored by Mrs. H. R. Peck. She was reclassified as a motor torpedo boat tender and redesignated AGP‑7 on 11 March 1943 and commissioned on 17 October 1943 with Commander D. B. Coleman in command.

United States Navy service[edit]

World War II[edit]

Following shakedown off southern California, Mobjack departed San Diego, California, for the Southwest Pacific on 14 December 1943. Steaming via New Caledonia and the New Hebrides, she arrived at Rendova, British Solomon Islands, on 14 January 1944 to begin duty with Motor Torpedo Boat Squadrons, South Pacific (SOPAC). She trained and supplied patrol torpedo boats (PT boats) in the New Georgia area until 6 March 1944, when she steamed to the Treasury Islands and thence to the motor torpedo boat base, Emirau, arriving on 23 March 1944. In mid‑May 1944 she returned to the Treasury Islands, where she overhauled PT boats and repaired and tended the motor gunboats (PGMs) and landing craft infantry gunboats (LCI(G)s) of Task Group 30.3 into July 1944.

Employed briefly in transporting spares and other materiel, she departed for British New Guinea on 23 July 1944, arriving at Dreger Harbor on 27 July 1944 to begin service under Commander, Motor Torpedo Boat Squadrons, 7th Fleet. During the greater part of August 1944 she operated at Aitape Harbor, tending Motor Torpedo Boat Squadron (MTBRBon) 33 and providing assistance in salvage work. On 28 August 1944, she got underway for Mios Woendi, Netherlands New Guinea, in company with MTBRBon 33. Arriving there on 31 August 1944, she was engaged in fueling, provisioning and making final repairs to the PT boats of the squadron preparatory to sailing for Morotai as a unit of Task Group 70.1.


Arriving at Morotai on 16 September 1944, the day after the American landings there, she commenced tending the boats of her squadron and Consolidated PBY Catalina flying boats assigned to air-sea rescue of pilots downed en route to and from raids on Truk. For the first three days she went about her duties unscathed in spite of Japanese air resistance.

At sunrise on 19 September 1944, however, a smoking Japanese fighter emerged from a heavy overcast and dove for Mobjack. Unable to crash into the ship, the pilot dropped two bombs which exploded close alongside, holing the deck and wounding one of her crew.

Making temporary repairs, she remained at Morotai, tending PT boats of Task Unit 70.1.2 and PBYs now ranging over the Netherlands East Indies on relief and intelligence and reconnaissance missions, until February 1945.

The Philippines[edit]

During February and March 1945, Mobjack transported materiel, spares, and advanced base personnel as she accompanied motor torpedo boat squadrons to forward areas. At Mios Woendi on 1 April 1945, she took on base force personnel of MTBRons 9 and 10 and on 2 April 1945 got underway for Samar in the Philippine Islands. Arriving on 11 April 1945, she disembarked her passengers and steamed on to Palawan, where she relieved motor torpedo boat tender USS Willoughby (AGP-9) as the repair unit for MTBRons 20 and 23. She moved on to Mangarin Bay, Mindoro, in mid‑May 1945 to overhaul and repair motor torpedo boats for use in the Philippines and in the upcoming Borneo operations.

The Borneo campaign[edit]

On 8 June 1945, Mobjack steamed to Samar to stage for the landings at Balikpapan on Borneo. Departing on 21 June 1945, she moved, with MTBRons 10 and 27, to Basilan Island, thence, on 26 June 1945, further down the Sulu Archipelago and into Makassar Strait. On 27 June 1945, she joined the minesweepers, at work since 1 June 1945, and the ships of the bombardment group, which had been pounding the Japanese-held oil center since 17 June 1945, in preparing the way for the Australian assault force. For four days Mobjack fueled and sustained the motor torpedo boats assigned to night patrol off the coast to prevent the Japanese from replacing naval mines, restoring obstacles blown by underwater demolition teams, or disturbing channel markers planted by the minesweepers. On 1 July 1945, these extensive preparations and precautions proved to have been well executed as wave after wave of personnel of the Australian 7th Division of the Australian I Corps went ashore without a casualty.

Mobjack, harassed by Japanese night air attacks until Royal Australian Air Force night fighters stopped them, remained outside the harbor for the next nine days. On 11 July 1945 she stood into the harbor, where, on 15 August 1945, she received a dispatch directing the cessation of all offensive action against the Japanese. World War II was over.

Honors and awards[edit]

Mobjack received three battle stars for World War II service.

Post-World War II[edit]

On 12 September 1945, Mobjack returned to the Philippines and for the next two months engaged in decommissioning motor torpedo boats under Commander, Motor Torpedo Boat Squadrons, Philippine Sea Frontier. On 10 November 1945 she headed eastward, arriving at San Francisco, California, on 29 November 1945.

In December 1945, stripping of Mobjack began, and on 21 August 1946 she was decommissioned. The Navy transferred her the same day to the United States Department of Commerce.

U.S. Coast and Geodetic Survey service[edit]

USC&GS Pioneer (OSS 31)
USC&GS Pioneer (OSS 31) passing under the Golden Gate Bridge ca. 1952.

The Department of Commerce placed the ship in service with the United States Coast and Geodetic Survey later in 1946 as the "ocean survey ship" USC&GS Pioneer (OSS 31), the third Coast and Geodetic Survey ship to bear the name.

Pioneer spent her Coast and Geodetic Survey career on duties in the Pacific Ocean. In August 1955, she received the first marine magnetometer, a towed magnetometer which Victor Vacquier of Scripps Institution of Oceanography had developed while conducting surveys for the U.S. Navy off the coast of California. She employed this magnetometer on a survey from Point Conception, California, to Cape Flattery, Washington, which went down in history as “The Pioneer Survey.” Her work with the magnetometer led to the collection of data which allowed the discovery of magnetic striping on the floor of the Pacific, and this proved to be a major discovery in the development of the theory of plate tectonics.

In 1964, Pioneer became the first U.S. Coast and Geodetic Survey vessel to operate in the Indian Ocean when she participated in the International Indian Ocean Expedition.

Final disposition[edit]

Pioneer was sold for scrap on 4 May 1966 to National Metal and Steel Corporation, Terminal Island, California.


Two geographic features on the floor of the Pacific Ocean, the Pioneer Fracture Zone and Pioneer Ridge, are named for Pioneer.