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.
Upon declaration of war, the United Kingdom, France, and Germany attempted to restrict their adversaries' ability to import raw materials and manufactured goods. The belligerent navies were deployed to intercept ships capable of carrying such imports. Ships evading enemy naval patrols in the open ocean faced a final gauntlet nearing the European Atlantic coast where belligerent warships and patrolling aircraft congregated around the United Kingdom adjacent to Germany's oceanic trade routes. The United Kingdom and France controlled extensive overseas territories in 1939, while Germany had lost its colonial empire as war reparations in 1919. French and British empire seaports and airfields allowed Allied warships and aircraft to patrol around the world, while German warships controlled very few locations where they might safely refuel and resupply, and German military aircraft operations were effectively limited to occupied territory. The United Kingdom and France had more warships than Germany; so German warships relied upon concealment, speed, or disguise to avoid destruction. U-boats were most numerous and active in European coastal areas, while a few German cruisers, battleships, and merchant raiders intercepted Allied shipping on ocean trade routes.
During World War I, outnumbered German warships had shifted patrol areas away from the United Kingdom into the Atlantic to disperse opposing Allied naval forces. After refueling at Newport, Rhode Island on 7 October 1916, U-53 sank five Allied merchant ships the following day in international waters off the coast of the United States. Although K/L Hans Rose scrupulously followed international law, the loss of American export cargoes incensed Americans as neutral United States Navy destroyers were obliged to stand aside while observing nearby merchant ships being sunk, and taking aboard seamen from the sunken ships.
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.
Despite the name, the Neutrality Patrol greatly favored the British as the Royal Navy had far greater access to the Atlantic. While German naval shipping and military aircraft could operate only from the coast of Europe to intercept British ships, German ships could be intercepted by British military forces operating from the United Kingdom, Canada, Newfoundland, Labrador, Gibraltar, Sierra Leone, Gambia, Nigeria, South Africa, British Togoland, the British Cameroons, the Falkland Islands, South Georgia, Saint Helena, Ascension Island, Bermuda, Jamaica, Trinidad, Barbados, The Bahamas, the British Leeward Islands, the British Windward Islands, the British Virgin Islands, British Honduras, and British Guiana.
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:
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.
The Royal Navy destroyer HMS Hyperion intercepted the German liner Columbus off Bermuda on December 19 after six days of radioed position reports by three relays of Neutrality Patrol destroyers shadowing the liner since it departed Veracruz. Roosevelt ordered all reports of the incident should indicate Hyperion encountered Columbus by chance. The Neutrality Patrol similarly radioed position reports of the British RFA tanker Patella a few days later, reasonably confident there were no German ships in position to intercept. The German freighter Konsul Horn left Aruba on January 7, 1940, posing as a Soviet ship to avoid identification by the Neutrality Patrol. The German freighter Helgoland sailed from Colombia on October 24, 1940, and evaded pursuit attempts by Neutrality Patrol destroyers. The German freighter Rio Grande similarly evaded the Neutrality Patrol by sailing from Rio de Janeiro on October 31; but USS Plunkett prevented German ships Orinoco and Phrygia from leaving Tampico, Mexico on November 15.
For each incident of the neutrality patrol reporting a British ship in the Gulf of Mexico, several German ships were intercepted by Royal Navy units responding to the American reports. Of the 211 German merchant ships attempting return to Germany during the last four months of 1939, only 32 (37%) of the 85 ships leaving the western hemisphere through the declared neutrality zone were successful, while 100 (80%) of the 126 leaving other parts of the world successfully evaded Allied interception.