At 13.20 hours on 11 April 1942 the unarmed Harry F. Sinclair, Jr. (Master William Collegan) was torpedoed by U-203 7 miles south of Cape Lookout, while steaming on a zigzag course at 13.5 knots with USS Herbert (DD 160) and a US Coast Guard boat as escort off the port quarter. A torpedo struck on the port side under the pump room between the #4 and #5 tanks.
The explosion immediately created a blazing inferno amidships and the crew of eight officers and 28 crewmen left the ship in three lifeboats and one raft, but the men in one of the lifeboats perished in the flames. Neither the radio operator nor any of the deck officers survived, a total of four officers (including the master) and six crewmen died. The survivors in the lifeboats were picked up about two hours later by HMS Hertfordshire (FY 176) and the two men on the raft were rescued by the destroyer. All survivors landed in Morehead City, North Carolina.

On 15 April, the burned out Harry F. Sinclair, Jr. was towed into Morehead City by HMS Senateur Duhamel (FY 327). She was eventually towed to Baltimore, arriving on 24 June, where the ship was repaired and returned to service in 1943 as Annibal.