At 16.24 hours on 9 July 1942 the unescorted Santa Rita (Master Henry R. Stephenson) was hit by one torpedo from U-172, while steaming on a nonevasive course at 16 knots about 700 miles northeast of Puerto Rico. Lookouts had spotted the wake but it was too late and the torpedo struck on the port side between #3 hatch and the engine room. The explosion killed one officer and two crewmen on watch below, wrecked the engines and opened a hole 30 feet in diameter that caused the flooding of the #3 hold. Ten minutes after the hit, the most of the eight officers, 44 crewmen, two passengers and nine armed guards (the ship was armed with one 5in and some .50cal and .30cal guns) abandoned ship in an orderly manner in the two starboard lifeboats, but one of them capsized and one crewman drowned. They were followed by the master, chief officer and ten men in a third boat.

The U-boat then surfaced and fired some machine gun burst to warn the survivors and fired four rounds from the deck gun into the superstructure and destroyed the radio room. Some Germans boarded the abandoned vessel, searched her and placed scuttling charges on board. They returned to the U-boat after two hours with some foodstuffs. The ship sank capsizing at 20.30 hours after the charges detonated and seven more shells were fired into the hull. The master was questioned by Emmermann and then taken on board as prisoner of war. He was landed in Lorient on 21 July, taken to Wilhelmshaven and from there to the POW camp Milag Nord near Bremen. He was repatriated on the Swedish motor merchant Gripsholm in January 1945 through a Red Cross exchange of prisoner of war.

32 survivors in two lifeboats were picked up on 11 July by USS Livermore (DD 429) and USS Mayo (DD 422) and landed at Port of Spain, Trinidad. The other lifeboat with 27 survivors was taken in tow by a US Army Air Force crash boat after being spotted on 25 July by an aircraft and landed at Borenquen Point, Puerto Rico.