The following morning U-546, commanded by Lt. Capt. Paul Just, began lining up an attack run on the escort carrier USS Core when the destroyer-escort USSFrederick C. Davis detected it and attempted to intervene. U-546’s acoustic homing torpedo struck the American vessel, breaking it in half in five minutes, losing 115 of its crew of 209. The nearby DEs swarmed around the submerged U-546 and pelted it with Hedgehogs for ten hours, until it finally surfaced. The badly damaged submarine was promptly blown to pieces by vengeful Allied shells.

In the closing weeks of World War II in Europe, American intelligence determined that a detachment of German submarines had been dispatched to launch a cruise missile attack on the East Coast of the United States. The U.S. Navy deployed forty-six ships and dozens of aircraft to annihilate the incoming submarine wolf pack. The battle that followed saw hundreds of lives lost at sea, and showed American intelligence services at their very best—and worst.

Nazi Germany was the first nation to deploy cruise and ballistic missiles in combat. The V1 “Buzz Bomb” could fly more than 180 miles powered by a pulse jet before slamming into its target. The slightly longer-range V-2 could shoot up to fifty-five miles high in its ballistic trajectory before plunging unstoppably towards the ground. Both weapons killed thousands of civilians in London and Western European cities. However, the United States remained far out of reach.

Nonetheless, the possibility that the so-called “vengeance weapons” might be mounted on submarines and used to sow chaos along the eastern seaboard of the United States did not escape Allied commanders. After the FBI interrogated a German spy rescued from a destroyed U-Boat, J. Edgar Hoover warned Washington on October 25, 1944, that Germany was planning a submarine-launched buzz bomb attack on the United States. Supposedly, reconnaissance photos depicted what appeared to be launch rails on U-Boats penned in Norway. Two more spies, arrested in December 1944, gave similar accounts of a submarine-launched missile program. In Berlin, minister of war production Albert Speer promised that missiles would fall on New York by February.

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Most Allied commanders were skeptical that there was a genuine threat to the continental United States—save for certain leaders of the U.S. Navy. In January 1945, the U.S. Atlantic Fleet organized two coastal defense task forces that would operate from a forward base in Argentia, Newfoundland. The fleet’s commander, Adm. Jonas Ingram, warned the press of probable “robot bomb” attacks launched by a “half-dozen submarines” in the coming months.

At the heart of each of the detachments were two escort carriers which could carry two dozen patrol planes each. Antisubmarine aircraft had proven highly effective at detecting surfaced U-Boats, and had sunk more than their fair share.

Accompanying the “jeep” carriers were more than twenty destroyer-escorts (DEs), small antisubmarine vessels equivalent to a modern frigate. Benefitting from sonar, radar and air patrols, the DEs were also armed with Hedgehogs—arrays of twenty-four spigot mortar charges that could be launched up to two hundred meters away. Unlike depth charges, Hedgehogs detonated on contact with a submarine’s hull, often sank the target in one or two hits, and could not be easily evaded after launch.

The U.S. Navy had a key advantage—the British had broken the German’s top-level code way back in 1941 and had been closely following the movements of German submarines since then, with the exception of a ten-month period in 1942 when the Kriegsmarine upgraded its encrypting machines.

In March, the Allies intercepted a message from German Admiral Godt dispatching seven Type IX long-range submarines to “attack targets in American coastal zone” as part of an attack group awesomely codenamed Seewolf. Another intercept message diverted to the U.S. coast the U-Boat of Captain Friedrich Steinhoff, who had earlier commanded U-511 in tests of rocket artillery that could be fired underwater.

The Navy was convinced that these signs all heralded an attack by missile-launching U-Boats, and sprang into action, initiating Operation Teardrop and diverting merchant traffic away from the battle zone. By April 12, the First Barrier force had established a “barrier line” 105 miles from north to south to screen for approaching submarines. A dozen DEs stood sentinel on the line, while the escort carriers and their escorts remained further back.

Meanwhile, the Kriegsmarine continuously micromanaged the approach vectors of its submarines via radio transmissions. These were intercepted by Allied intelligence, giving the U.S. Navy a fairly good idea of where the U-Boats were approach from. However, bad weather prevented the aircraft aboard the escort carriers from patrolling as actively as desired

The diesel-powered Type IX submarines could travel underwater a maximum of only sixteen hours at roughly 4.5 miles per hour before their batteries ran dry. Therefore, the German submarines typically surfaced at night to move at much higher speeds and recharge their batteries—but still did so at a risk.

On April 15, the submarine U-1235 was detected on radar shortly after midnight, about midway between the coasts of France and Newfoundland. Though it quickly submerged, the U-Boat was sunk under a sustained Hedgehog attack by the USS Stanton and USS Frost.

Just a few hours later, U-880 too was intercepted on the surface by the Frost and raked by forty-millimeter antiaircraft guns at short range. Though the U-Boat managed to submerge, it succumbed to a sustained depth charge attack shortly afterwards. Both submarines exploded catastrophically without leaving behind any survivors, reinforcing suspicions that they were carrying missiles.

Another U-Boat was spotted by a B-24 patrol bomber on April 19, but managed to escape, and a fourth submarine managed to dodge pursuing destroyers. However, two days later around midnight, U-518 was detected by sonar and sunk after it was struck by Hedgehogs launched from the USS Neal Scott and Carter.

These losses caused the German Navy to disperse the survivors of Seewolf on vectors towards New York and Hamilton, and divert three additional U-Boats to reinforce their attack. By then, the slightly larger Second Barrier Force had deployed in a line abreast. One of the force’s TBF Avenger torpedo bomber spotted U-881 around midnight on April 23, but failed to sink the vessel with its depth charges.

The following morning U-546, commanded by Lt. Capt. Paul Just, began lining up an attack run on the escort carrier USS Core when the destroyer-escort USSFrederick C. Davis detected it and attempted to intervene. U-546’s acoustic homing torpedo struck the American vessel, breaking it in half in five minutes, losing 115 of its crew of 209. The nearby DEs swarmed around the submerged U-546 and pelted it with Hedgehogs for ten hours, until it finally surfaced. The badly damaged submarine was promptly blown to pieces by vengeful Allied shells.

Nonetheless, thirty-three survivors were rescued, including Captain Just, who was photographed coming on board the escort carrier USS Bogue. American interrogators were convinced that additional U-Boats were still creeping towards the East Coast to unleash a deadly missile barrage—but Just and his officers did not provide any information confirming that.

What followed was one of the few occasions that the U.S. military tortured prisoners during World War II. Captain Just and eight specialists from U-546 were placed in solitary confinement, beaten, deprived of sleep and forced to perform grueling exercise routines. These interrogations continued on U.S. soil until May 12, four days after the German surrender.

Operation Teardrop was not finished quite yet, however. The Second Barrier Force dispersed to cover a wider area and combed the waters westward towards American shores, reinforced by an additional escort carrier group. Shortly before dawn on May 5, sonar onboard the destroyer-escort USS Farquhar detected U-881 underwater. Farquhar promptly dispatched the submarine with a depth-charge attack—claiming the last German submarine sunk by the U.S. Navy during World War II.

On May 8, Nazi Germany surrendered unconditionally. Amongst the many U-Boats notified to stand down was U-873, commanded by Friedrich Steinhoff, the man associated with the submarine rocket-launching tests. After surrendering to the USS Vance, Steinhoff and his crew were imprisoned in the Charles Street Prison in Boston. Steinhoff, described as “arrogant” and “menacing” by his Office of Naval Intelligence interrogators, was beaten and slapped until bloody. Two days later, he committed suicide using the cracked lenses of his sunglasses.

As it turned out, there were no U-Boats with missiles. The Kriegsmarine had dispatched Seewolf towards American shores to lower the pressure on its submarine operations in European waters.

The three-hundred-millimeter rockets Steinhoff had tested in 1942 were basically short-range unguided artillery. Though they could be fired from underwater, they were impossible to aim effectively and degraded the submarine’s seaworthiness, so the Kriegsmarine abandoned their development.

Later in November 1944, the Kriegsmarine began designing a launch container for V-2 ballistic missiles that would have been towed by a U-Boat off the East Coast. Construction of the first device theoretically concluded in Stettin around the same time as Operation Teardrop went into action, but like many desperate projects initiated in the final days of the Third Reich, nothing ever came of it. Nazi Germany never had any guided missile-launching submarines.

Aided by bountiful signals intelligence, Operation Teardrop succeeded in knocking out four of the seven submarines in Seewolf, and one of the three vessels sent as reinforcements. The U-Boats were intercepted both on the surface and submerged, reflecting the refinements in technology and tactics the U.S. Navy had implemented after the costly early years of the Battle of the Atlantic.

The U.S. Navy responded with overwhelming force against a potential threat to the continental United States—but proved too willing to bend its principles on the treatment of prisoners of war, escalating the use of torture when the prisoners did not confirm the interrogator’s incorrect assumptions, as often happens.

Ironically, it would actually be two U.S. submarines that first tested submarine-launched cruise missiles two years later. The weapon: an American copy of the V-1 buzz bomb.

Sébastien Roblin holds a Master’s Degree in Conflict Resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring.

This article was originally published in 2016.