At 08.57 hours on 4 Dec 1943 the unarmed Libertad (Master Moisés Gondra Urrutia) in station #13 of convoy KN-280 was hit on the port side at #4 hold and further back on the port quarter by two of four torpedoes from U-129, developed a heavy list to port and sank very rapidly by the stern about 75 miles south-southeast of Cape Hatteras. The U-boat escaped after the attack on the surface without being engaged by the escorts of convoy. Unknown to the Germans the ship sank so fast in the rainy and moonless night that none of the other ships in convoy noticed what happened. The ship had originally been in station #34, but was reassigned to station #13 the day before the attack after two ships became stragglers. The crew had no time to send distress signals and the ship sank underneath them while they tried to launch two lifeboats. Twelve men swam to two rafts and lashed them together, four more climbed on a capsized lifeboat and at least nine men clung to drifting planks and other wreckage. The survivors attempted to attract attention with a hand flashlight and by lighting a sodium compound spread on the water but in vain.

Only at daybreak it was discovered that the Libertad was missing from convoy and USS Natchez (PF 2) and USS PC-564 were sent from Norfolk to search the area, furthermore USS SC-1306 and USS SC-1358 were ordered to sweep convoy route. Dispatched were also three PV Ventura aircraft from Cherry Point, a PBM Mariner from Norfolk, a Hall flying boat from Elizabeth City and two blimps from Weeksville. At 18.35 hours on 5 December, the blimp K-82 (Ens Frank J. Hudner, USNR) located men clinging to drifting wreckage in position 34°40N/74°53W and dropped emergency rations and a life raft. They were picked up after four hours by USS Natchez, which also picked up the twelve men on the two rafts after they were spotted by the blimp K-72 (Lt John Marck, USNR) in position 34°33N/74°58W. The four vessels then formed a scouting line to search for further survivors during the night, but USS SC-1306 (Lt R.L. Thayer, USN) was damaged in a collision with USS PCE-869 and could no longer participate. In the morning of 6 December, the blimp K-76 (Lt David T. Breault, USN) sighted the four men clinging to the upturned lifeboat in position 34°44N/74°50W and homed USS Natchez to their position. The frigate and USS SC-1358 continued their search until the evening of 7 December, though much debris and wreckage was seen, no further survivors were found. All survivors were then transferred to the submarine chaser which landed them in Morehead City. They were first transported to Norfolk for a hearing, then traveled by train to Miami from where they were repatriated to Havana aboard three Cuban submarine chasers.