Thomas McKean was laid down on 5 November 1941, under a Maritime Commission contract, MCE hull 301, by the Bethlehem-Fairfield Shipyard, Baltimore, Maryland; and was launched on 30 April 1942.

[4] Thomas McKean had set out on her maiden voyage from Philadelphia, in June 1942, for Bandar Shapur, Iran, with 9,000 LT (9,100 t) of Lend-Lease war supplies, that included tanks, food, and 11 aircraft.

At 13:55, on the afternoon of 29 June 1942, while steaming unescorted in a zigzag course at 10 kn (19 km/h; 12 mph), Thomas McKean was struck by two torpedoes fired from the German submarine U-505, at 22°00′N 60°0′W / 22.000°N 60.000°W / 22.000; -60.000, about 350 nmi (650 km; 400 mi) northeast of Puerto Rico.

One of the torpedoes struck aft of hold #5, destroying the stern 4-inch (100 mm)/50 caliber gun and killing three armed guards.

The captain, Mellin Edwin Respess, ordered the crew of eight officers, 31 crewmen, 17 armed guards, and four passengers to abandon ship in the four lifeboats.