On September 3, 1939, the British and French declarations of war on Germany initiated the Battle of the Atlantic. The United States Navy Chief of Naval Operations (CNO) established a combined air and ship patrol of the United States Atlantic coast, including the Caribbean, on September 4. President Franklin D. Roosevelt declared the United States' neutrality on September 5, and declared the naval patrol a Neutrality Patrol. Roosevelt's initiation of the Neutrality Patrol, which in fact also escorted British ships, as well as orders to U.S. Navy destroyers first to actively report U-boats, then "shoot on sight", meant American neutrality was honored more in the breach than observance.
On September 4, 1939, the Chief of Naval Operations (CNO) ordered the Atlantic Squadron to establish a combined air and ship patrol to observe and report the movements of ships of warring nations within a line extending east from Boston to 65 degrees west and thence south to the 19th parallel and seaward around the Leeward and Windward Islands. The concept of a naval Neutrality Patrol within that zone was presented to a Conference of Foreign Ministers of the American Republics convened in Panama on September 25. After considerable debate, the conference agreed the Declaration of Panama on October 2, 1939, to extend the neutrality zone southwesterly parallel to the northeastern coast of South America approximately 300 miles (480 km) offshore.
Battleships USS Arkansas, Texas, and New York with the aircraft carrier USS Ranger (with aircraft squadrons VB-4, VF-4, VS-41, and VS-42 embarked) formed a reserve force at Hampton Roads to support the following patrols:
- Patrol Zero: Destroyer division 18 of USS Davis, Jouett, Benham, and Ellet were assigned patrol station zero from Newfoundland south to the 40th parallel.
- Patrol One: Destroyers USS Hamilton and Leary were assigned patrol station one along a northwest-southeast line off Georges Bank.
- Patrol Two: Destroyers USS Hopkins and Goff, with aircraft of patrol squadron VP-54 and seaplane tender USS Owl, operated from Newport, Rhode Island, between the 38th and 43rd parallels.
- Patrol Three: Destroyers USS Manley, Barry, Decatur, and Reuben James patrolled between the 34th and 38th parallels with aircraft of VP-52 and VP-53.
- Patrol Six: Destroyers USS Babbitt and Claxton patrolled the Florida Strait and Yucatán Channel.
- Patrols Seven and Eight: Cruisers USS San Francisco and Tuscaloosa with destroyers USS Broome, Borie, Simpson, and Truxton patrolled the eastern Caribbean south of the 23rd parallel with aircraft of VP-33 and VP-51 supported by seaplane tenders USS Lapwing, Gannet, and Thrush. Gannet and Thrush established a seaplane base in Puerto Rico.
- Patrol Nine: Cruisers USS Quincy and Vincennes patrolled within 300 miles (480 km) of the coast between Newport and Cape Hatteras.
The CNO orders of September 4 directed the patrols to report the movements of ships of warring nations in cipher. U.S. Navy ships were initially instructed to avoid making any report while in the vicinity of such ships to avoid performance of unneutral radio direction finding service or the impression that an unneutral service was being performed. On October 9, President Roosevelt instructed the navy to transmit reports promptly in plain English; and the Neutrality Patrol was instructed on October 20 to report contacts with plain-language radio transmissions.
Neutrality Patrols began operating from Bermuda following the Destroyers for Bases Agreement. The base was commissioned on April 7, 1941; and Carrier Division 3 (USS Ranger, Wasp, and Yorktown) began using the base the following day. By mid-June cruisers USS Memphis, Milwaukee, Cincinnati and Omaha were patrolling from Trinidad south along the coast of Brazil.
At the beginning of 1941, President Roosevelt secretly organized a protection-of-shipping task force 24, given the designation of Support Force, United States Atlantic Fleet, under the command of Rear Admiral Arthur L. Bristol. Ships, planes, funding, and personnel were assigned in January and February, and operations began in March. Admiral Bristol remained in Washington, but material for the various bases was assembled and shipped from Naval Air Station Quonset Point. Admiral Bristol insisted that all records be destroyed when an operation was completed. His staff believed he was following Presidential instructions to avoid revealing operations which might not have public-opinion approval. Efforts to document Support Force operations after the war were discouraged to avoid damaging world opinion as to the integrity of United States' neutrality.
To augment the fleet units already engaged in the Neutrality Patrol which President Roosevelt had placed around the eastern seaboard and Gulf ports, the United States Navy recommissioned 77 destroyers and light minelayers which had lain in reserve at either Philadelphia or San Diego. In Newfoundland on August 9, 1941, President Roosevelt agreed to provide American destroyers as escorts for the Canada to Iceland portion of HX convoys and westbound ON convoys. USS Greer ineffectively engaged U-652 on September 4; and on September 11 President Roosevelt declared Axis ships entered the neutrality zone at their own risk, and ordered the U.S. Navy to attack any vessel threatening ships under American escort. HX 150 sailed September 16, 1941, as the first convoy with American escort. ON 18 sailed September 24 as the first westbound convoy with American escort. The Gleaves-class destroyer Kearny was torpedoed while escorting Convoy SC 48 on October 17, 1941. The destroyer Reuben James was torpedoed and sunk on October 31, 1941, while escorting Convoy HX 156 with a loss of 100 lives.
The Neutrality Patrol was a major focus of one of the world's largest navies for the first third of the Second World War. The Atlantic Squadron in that period consisted of three battleships, four heavy cruisers, 29 destroyers, and one aircraft carrier; and their primary mission was confirmed by its being redesignated the Patrol Squadron on 1 November 1940. The Neutrality Patrol enhanced effectiveness of Allied patrols within the declared neutrality zone. On 12 July 1940, Assistant CNO Robert L. Ghormley was ordered to Britain to standardize shipboard communications between British and American warships.
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- "Strict Neutrality – Britain and France at War with Germany: September 1939 – May 1940". United States Navy and World War II. Naval-History.net. Archived from the original on 2006-11-18. Retrieved 2007-05-14.
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- Neutrality (Declaration of Panama), 3 October 1939