In late 1944, the Allies received intelligence reports which suggested that Germany's Kriegsmarine was planning to use V-1 flying bombs launched from submarines to attack cities on the east coast of the United States.

In September of that year, Oskar Mantel, a spy captured by the U.S. Navy when the submarine (U-1229) transporting him to Maine was sunk, told his FBI interrogators that several missile-equipped U-boats were being readied.

United States Tenth Fleet analysts subsequently examined photos of unusual mountings on U-boats at bases in Norway, but concluded that they were wooden tracks used to load torpedoes.

The British Admiralty discounted these reports, and assessed that while V-1s could be potentially mounted on Type IX submarines, the Germans were unlikely to devote scarce resources to such a project.

[2] Despite the Tenth Fleet and Admiralty assessments, the U.S. military and government remained concerned that Germany would conduct vengeance attacks against East Coast cities.

[3] In late December 1944, the spies William Curtis Colepaugh and Erich Gimpel, who had been captured in New York City after being landed by U-1230 in Maine, told their interrogators that Germany was preparing a group of rocket-equipped submarines.

[4] Despite this, the Department of War, which was dominated by the United States Army, advised President Franklin D. Roosevelt on 11 December that the threat of missile attack was so low that it did not justify the diversion of resources from other tasks.

[3] In response to the perceived threat, the U.S. Atlantic Fleet prepared a plan to defend the east coast from attacks by aerial raiders and missiles.

The centerpiece of the plan was the formation of two large naval task forces to operate in the mid-Atlantic as a barrier against submarines approaching the east coast.

These task forces were formed from several existing escort carrier groups, and used Naval Station Argentia, Newfoundland, as their forward operating base.

As well as guarding against missile attacks, these large forces were tasked with countering the new and high-performance Type XXI submarines if they began operating in the central Atlantic.

[5] In January 1945, German Minister of Armaments and War Production Albert Speer made a propaganda broadcast in which he claimed that V-1 and V-2s "would fall on New York by February 1, 1945", increasing the U.S. Government's concern over the threat of attack.

Vulkan Docks in Stettin was contracted to build a prototype in March or April 1945, but little work took place before Germany's final collapse.

Vice Admiral Ingram and the U.S. Tenth Fleet concluded that the boats in Group Seewolf were carrying V-1s and launched Teardrop in response.

After illuminating the submarine with star shell and spotlights, the destroyer escort opened fire on her with Bofors 40 mm guns from a range of 650 yards (590 m) at 02:09.

[19] Even though Teardrop was undertaken in the part of the North Atlantic for which Canada had primary responsibility, Ingram did not seek assistance from the Royal Canadian Navy (RCN) at any stage of the engagement.

[21] On the night of 22–23 April, U-boat Command dissolved Group Seewolf and directed the three surviving boats to take up stations between New York and Halifax.

Radio signals directing these deployments were decrypted by Allied code breakers and increased fears that the submarines were trying to attack American cities.

[19] The Second Barrier Force encountered its first U-boat on 23 April when a Grumman TBF Avenger from VC-19 sighted U-881 about 74 nautical miles (137 km) north west of Bogue just after noon.

The eight men were transferred to Fort Hunt, Virginia shortly after VE Day, where they continued to be harshly treated until Just agreed to write an account of U-546's history on 12 May.

[26] Historian Philip K. Lundeberg has written that the beating and torture of U-546's survivors was a "singular atrocity" motivated by the interrogators' need to promptly extract information on potential missile attacks.

Following the end of World War II in Europe that day, it accepted the surrender of U-234, U-805, U-858 and U-1228 at sea before returning to bases on the U.S. east coast.

[30] Kapitänleutnant Fritz Steinhoff, who had commanded U-511 during her rocket trials and was captured at sea when he surrendered U-873, was subjected to an abusive interrogation at Portsmouth by the interviewers of U-546's crew.

An official Navy investigation was held into this interrogation after Steinhoff committed suicide at Charles Street Jail in Boston shortly afterwards.

[30] Other after action reports stressed the importance of teamwork between destroyer escorts when attacking submarines and argued that single barrier lines such as those used throughout most of Teardrop were inferior to grouping ships in assigned patrol areas.

"[34] Similarly, the British official history of the role intelligence played in World War II noted that information obtained from decrypted German radio transmissions contributed to "virtually all" of the sinkings during Teardrop.