At 05.56 hours on 17 March 1943, U-600 (Zurmühlen) fired a spread of four FAT torpedoes at convoy HX-229 in 50°36N/34°30W and observed a hit amidships on the Nariva in station #91 and two on the Irénée Du Pont in station #81. A further detonation was heard, this was the hit on the Southern Princess in station #72, which caught fire and sank during the morning. At 05.58 hours, the stern torpedo was fired and was seen to hit another freighter amidships, which sank after 10 minutes, but this can not be confirmed from Allied sources. At 08.39 hours the same day, U-91 fired a spread of three torpedoes at some ships behind convoy in 50°38N/34°46W and noted two hits, one on a moving freighter and the other on a burning ship. These hits finished off Nariva and Irénée Du Pont and their sinking in 51°05N/33°55W was observed by U-91 in the afternoon and reported at 16.08 hours by a radio message.

The Irénée Du Pont (Master Christian Boel Simonsen) was struck by two torpedoes on the starboard side at holds #2 and #3. The explosions knocked out the generators, flooded both holds and also flooded slowly the engine room and hold #1. The ten officers, 39 crewmen, 26 armed guards (the ship was armed with one 5in, one 3in and eight 20mm guns) and nine passengers (naval personnel) abandoned ship 45 minutes after the hits in two lifeboats and three rafts. Some of the men jumped overboard because a third lifeboat fouled a cargo net and other rafts could not be launched. Six armed guards, six crewmen and one passenger drowned. The British steam merchant Tekoa in station #84 stopped, picked up 55 survivors and later landed them in Liverpool. HMS Mansfield (G 76) (LtCdr L.C. Hill, OBE, RNR) rescued 16 others, of which one later died from shock and was buried at sea. HMS Anemone (K 48) (LtCdr P.G.A. King, RNR) tried to sink the ship with 4in gunfire and a depth charge, but the ship remained afloat and was later finished off by U-91.

The master of the Irénée Du Pont asked to leave convoy since his ship could steam at 16 knots, but this permission was denied.