Yes, several ships carrying American troops were torpedoed and sunk by U-boats during WWII. The SS Dorchester was sunk in February 1943 by the U-boat U-223, while carrying American troops to Greenland. She was carrying just over 900 men, with 675 casualties. Another sinking was the sinking of the SS Leopoldville on Christmas Eve 1944. The Leopoldville was a Belgian transport. She was carrying 2,200 men from the 262nd and 264th Regiments of the 66th Division, US Army, to Cherbourg as reinforcements for the Battle of the Bulge. She formed part of Convoy WEP-3, along with another troopship, the Cheshire. The two ships were escorted by two British destroyers and two frigates (one British and one French). At 17:54, she was struck on the starboard side, aft, by a torpedo from U-486. This flooded the Number 4 hold, and adjoining compartments, killing most of the 300 men in them. The remaining troops began to form up in good order on the ship's deck. Evacuation of the ship was delayed until 18:25, when HMS Brilliant, one of the escorting destroyers, came alongside, at considerable risk to herself, because the Leopoldville had begun to drift into a minefield. The ships were also tossed by heavy seas, while Leopoldville's lifeboats (still shipped), made it difficult for Brilliant to come alongside. As the two ships were tossed together, men had to jump from one ship to another. The evacuation was made more difficult by communications issues between the British ships of the convoy and the American forces at Cherbourg. The British ships had to communicate with their base at Portsmouth, because the RN were using different codes and radio frequencies from the Americans. A further issue was the Christmas holiday itself, with many of the ships in Cherbourg harbour being lightly manned and unready to sail as a result. At 19:20, Brilliant was forced to pull away, having rescued about 500 men. As she entered Cherbourg, she passed the first ships heading to the Leopoldville. By 20:00, the captain, a Belgian named Limbor, ordered his crew to abandon ship, leaving few with any experience of seamanship aboard - when the American tug ATR-3 threw ropes aboard, nobody had any clue what to do with them until one man made a stab at securing them. Limbor did not abandon ship, instead roaming the decks to advise on the evacuation. This was rather unhelpful, as he spoke mainly French and Flemish, languages not spoken by the average US infantryman. At around 20:30, two underwater explosions presaged the sinking of the Leopoldville, with hundreds of men aboard. Most of these made it into the water, but here, survival was tricky. The water was frigid, just 9^o C, while the men were mostly wearing their full gear and had not been trained to enter the water. In total, 763 Americans died, either aboard the Leopoldville or in the water, along with Limbor, four of his crew, and a few British officers.