'Teardrop' was a US naval undertaking against U-boats believed to be approaching the east coast of the USA for the launch of V-1 flying bombs (April/May 1945).

Two major US task forces were created, and these sank five U-boats, of which none was equipped to launch missiles, for the loss of the destroyer escort Frederick C. Davis with most of her crew.

Late in 1944, the Allies received intelligence reports suggesting that the German navy was planning to use V-1 flying bombs launched from U-boats to attack cities on the eastern seaboard of the USA. In September 1944 Oscar Mantel, a spy captured by the US Navy when the U-boat transporting him to Maine was sunk, told his Federal Bureau of Investigation interrogators that several missile-equipped U-boats were being readied. Analysts of Admiral Ernest J. King’s 10^th Fleet, which used Atlantic Fleet warships as and when required, then examined photographs of unusual mountings on U-boats at bases in Norway, but concluded that they were wooden tracks used to load torpedoes. Further rumours of missile-armed U-boats emerged later that year, including one from Sweden passed on by the Supreme Headquarters Allied Expeditionary Force. The British Admiralty discounted these reports, and assessed that while it was theoretically feasible for the V-1 to be mounted on a 'Type IX' class U-boat, the Germans were unlikely to devote scarce resources to such a project.

Despite the 10^th Fleet and Admiralty assessments, the US military and government remained concerned that Germany would conduct vengeance attacks against east-coast cities. Early in November 1944, the Eastern Sea Frontier therefore mounted an intensive search for U-boats within 250 miles (400 km) of New York City. Early in December 1944 the spies William Curtis Colepaugh and Eric Gimpel, who had been captured in New York City after being landed by Kapitänleutnant Hans Hilbig’s U-1230 in Maine, also told their interrogators that Germany was preparing a group of missile-equipped submarines. On 10 December Fiorello La Guardia, the mayor of New York, publicly warned that Germany was considering an attack on his city with long-range rockets. La Guardia’s warning and the claims made by the captured spies received considerable media coverage. Despite this, the army-dominated Department of War 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. This assessment was not supported by the US Navy.

In response to the perceived threat, the Atlantic Fleet prepared a plan to defend the east coast against attacks by aerial raiders and missiles. This plan was originally codenamed 'Bumblebee' but later renamed 'Teardrop'. Completed on 6 January 1945, the plan involved US Navy anti-submarine forces as well as USAAF and US Army units, which were to be responsible for shooting down attacking aircraft and missiles. The core of the plan was the establishment of two large naval task forces to operate in the mid-Atlantic as a barrier against U-boats approaching the east coast. These task forces were formed from several existing escort carrier groups, and used Argentia, Newfoundland, as their forward operating base.

As well as guarding against missile attacks, these substantial forces were tasked with countering the new and high-performance 'Type XXI' class U-boats should these begin to operate in the central Atlantic. The Atlantic Fleet’s commander, Vice Admiral Jonas H. Ingram, gave a press conference on 8 January in which he warned that there was a threat of missile attack and announced that a large force had been assembled to counter seaborne missile-launch boats.

In January 1945 Albert Speer, the German minister of armaments and war production, made a propaganda broadcast in which he claimed that V-1 flying bombs and V-2 ballistic missiles 'would fall on New York by 1 February 1945', thereby increasing the US government’s concern over the threat. However, the Germans had no ability to fire missiles from their submarines, as both attempts to develop submarine-launched weapons ended in failure.

In June 1942 Kapitänleutnant Friedrich Steinhoff’s U-511 was used for trials of small, short-range artillery rockets which could be fired while the boat was submerged, but all development of this system ended in early 1943 after it had been learned that the installation of the system degraded the U-boat’s seaworthiness.

The Germans also embarked in November 1944 on the development of a V-2 sealed launch canister that could be towed by a U-boat: aligned horizontally in the water for towing, the canister was then to have its base flooded to tilt the canister into the vertical position before its top was opened for the launch of the missile. Such canister launchers were to be towed to a position off the US east coast for a missile bombardment of New York. The Vulkan yard of Stettin was contracted to build a prototype in March or April 1945, but little work had been completed before Germany’s surrender in May 1945.

In March 1945, nine 'Type IX' class U-boats were dispatched from Norway to patrol off Canada and the USA, and on 12 April seven of these boats (Oberleutnant Hans-Werner Offermann’s U-518, Kapitänleutnant Paul Just’s U-546, Korvettenkapitän Richard Bernardelli’s U-805, Korvettenkapitän Thilo Bode’s U-858, Kapitänleutnant Gerhard Schötzau’s U-880, Kapitänleutnant Dr Karl-Heinz Frischke’s U-881 and Kapitänleutnant Franz Barsch’s U-1235) were designated as the 'Seewolf' (iii) wolfpack and ordered to attack shipping heading to the south from New York. The remaining two boats (Oberleutnant Otto Wermuth’s U-530 and Oberleutnant Erich Krempl’s U-548) were ordered to attack shipping in Canadian waters.

The Allies were aware of the boats' departure and destination through information gathered from 'Ultra' decrypts. Ingram and the 10^th Fleet concluded that the 'Seewolf' (iii) boats were carrying V-1 flying bombs and began 'Teardrop'. The ships of the 1^st Barrier Force, which comprised the escort carriers Mission Bay and Croatan as well as 20 destroyer escorts, sortied from Hampton Roads, Virginia, between 25 and 27 March, steamed to Argentia to refuel and assembled to the east of Cape Race on 11 April. Then 12 of the destroyer escorts deployed into a line 120 miles (190 km) long while the two carriers, each protected by four destroyer escorts, patrolled to the west of the line. The carriers' air operations were greatly hindered by heavy seas, however.

As they headed west, the 'Seewolf' (iii) boats were instructed to attack shipping, but found no targets as the Allies had routed the convoys of this period well to the south to avoid the severe weather and the attentions of the U-boats. The boats started to reach their initial stations, to the east of the Grand Banks of Newfoundland, during 8 April, and Grossadmiral Karl Dönitz, the commander-in-chief of the German navy, allocated the 'Seewolf' (iii) wolfpack a dozen different scouting lines between 2 and 19 April. The radio signals directing these deployments were intercepted and decrypted by the Allies, providing them with accurate information on where the boats were operating.

Just before 24.00 on 15 April the destroyer escort Stanton detected U-1235 in a position about 500 miles (805 km) to the north of Flores island, on radar and immediately attacked with her 'Hedgehog' anti-submarine mortar, but missed as the boat submerged. Assisted by Frost, Stanton quickly gained sonar contact and made three more 'Hedgehog' attacks. The third attack, at 00.33 on 16 April, sank the boat with the loss of her entire crew. Shortly after this Frost detected U-880 on radar as the boat sought to flee the area on the surface. After illuminating the submarine with star shell and spotlights, the destroyer escort opened fire on her at 02.09 with 40-mm cannon at a range of only 650 yards (590 m). U-880 quickly submerged but was tracked by Stanton's and Frost's sonar operators. The two ships made several 'Hedgehog' attacks on the boat, Stanton sinking it with no survivors at 04.04. Both boats suffered huge explosions after being struck by 'Hedgehog' projectiles, and this further raised the fear that they were carrying rockets.

The 1^st Barrier Force moved to the south-west after the destruction of these first two U-boats. Then Consolidated B-24 Liberator long-range patrol aircraft of VPB-114, equipped with a powerful 'Leigh Light' searchlight, spotted U-805 on the surface during the night of 18/19 April. The boat was only 50 miles (80 km) from Mission Bay and her escorts, but was not attacked as the patrol bomber was unable to establish whether or not the boat was German before she submerged. On the night of 20 April, U-546 attempted to torpedo a destroyer escort but missed. During the following night U-805 was detected by Mosley, but escaped after being depth charged over a two-hour period by Mosley, Lowe and J. R. Y. Blakely.

The 1^st Barrier Force scored its final success on the night of 21/22 April. Just before 24.00 Carter gained sonar contact with U-518. Neal A. Scott joined Carter and made the initial 'Hedgehog' attack on the boat. Carter then made her own 'Hedgehog' run, which sank U-518 with no survivors. By this time the 1^st Barrier Force was returning to Argentia as the 2^nd Second Barrier Force relieved it.

This fresh force comprised the escort carriers Bogue and Core together with 22 destroyer escorts. Bogue and 10 destroyer escorts had departed Quonset on 16 April, while Core and 12 destroyer escorts had departed Bermuda and other locations. The force was initially stationed along the 45° W in a patrol line 105 miles (170 km) long, and sailed toward the east. The line was made up of 14 destroyer escorts at 5-mile (8-km) intervals, with Core and her four escorts at its northern end and Bogue and her four escorts at the southern end.

On the night of 22/23 April, the U-boat command dissolved the 'Seewolf' (iii) wolfpack and directed the three surviving boats to take up stations between New York and Halifax. Shortly after this, U-881, U-889 and U-1229, which had been operating separately, were also ordered to positions between New York and Cape Hatteras. Radio signals directing these deployments were decrypted by Allied codebreakers and increased fears that the submarines were trying to attack US cities.

The 2^nd Barrier Force encountered its first U-boat on 23 April when a Grumman TBF Avenger of the VC-19 squadron sighted U-881 about 75 miles (120 km) to the north-west of Bogue just after 12.00. The aeroplane dropped depth charges, but did not seriously damage the submarine. On the following day U-546 sighted Core, manoeuvred to attack the escort carrier but, as it tried to pass through the barrier line, was detected at 08.30 by Frederick C. Davis, which immediately prepared to attack the boat. After realising that his boat had been detected, Just fired an acoustic-homing torpedo at the destroyer escort from a range of 650 yards (590 m). Frederick C. Davis's 'Foxer' decoy was not effective, and the torpedo struck her forward engine room at 08.35. She sank five minutes later with the loss of all but 66 of her 192-man crew. Eight destroyer escorts subsequently hunted U-546 for almost 10 hours before Flaherty severely damaged it with a 'Hedgehog' salvo. The boat immediately surfaced, but sank after Flaherty and three or four other destroyer escorts fired on it. Just and 32 other members of his crew survived the sinking and were taken prisoner.

Some of U-546's survivors were harshly treated in an attempt to force them to divulge whether or not the submarines bound for the US east coast were carrying missiles. After brief interviews on board Bogue, the survivors were transferred to the US base at Argentia. Upon arrival on April 27 the prisoners were screened for interrogation, eight specialists being separated from the other 25 survivors, who were then sent to prisoner of war camps. The specialists were held in solitary confinement and subjected to 'shock interrogation' techniques, including exhausting physical exercise and beatings. On 30 April Just provided brief information on the composition and mission of the 'Seewolf' (iii) wolfpack following a second interview, during which he collapsed unconscious. The information provided by Just and the other specialists did not mention whether or not the boats were equipped with missiles. The eight men were transferred to Fort Hunt, Virginia shortly after VE-Day, where they continued to be harshly treated until 12 May, when Just agreed to write U-546's history.

The 2^nd Barrier Force moved slowly to the south-west from 24 April as it searched for the remaining U-boats. Swenning made radar contact with a U-boat on the night of 24 April, but this escaped during the resulting search. After a week of searching to the south of the Newfoundland Banks, the barrier force was split on 2 May to provide a greater depth of search. The Mission Bay group reinforced the 2^nd Barrier Force during this period, increasing its strength to three escort carriers and 31 destroyer escorts.

On 5 May U-881 became the fifth and final boat sunk during 'Teardrop'. The boat was detected by Farquhar while attempting to pass submerged through the barrier line just before the break of day. The destroyer escort immediately turned to starboard and dropped depth charges, which sank the boat with all its crew at 06.16. U-881 was the last German submarine to be sunk by the US Navy in World War II.