At 06.07 hours on 7 July 1943, U-185 attacked convoy BT-18 about 175 miles east of Fortaleza, Brazil for a first time and reported two ships sunk and another damaged. In fact, the William Boyce Thompson and the James Robertson were sunk.

The James Robertson (Master Harold Fletcher DeLasaux) in station #21 was struck by two torpedoes in the #2 and #3 holds. The explosions destroyed the engine room bulkhead and blew several hatch covers off, littering the deck with bits of metal, rock ballast and pieces of lifeboats. The holds flooded to the tween decks and the ship buckled at the #3 hatch. The ship cut through the columns of convoy with running engines and the rudder jammed at hard right, making a complete circle. The ship collided first with the American steam merchant Alcoa Banner in station #32 and moments later with the Brazilian steam merchant Goiazloide in station #33 at the #1 hatch.

A part of the eight officers, 36 crewmen and 25 armed guards (the ship was armed with one 4in and nine 20mm guns) was ordered to abandon ship in two lifeboats and rafts. One boat swamped during launching and others jumped overboard and swam to the rafts, one of the armed guards drowned. The 21 men on the rafts, the men in one of the boats and five men in the water were picked up by USS PC-575 and landed at Trinidad on 15 July. The master and 20 men abandoned ship after the collision in two lifeboats and stood by until the morning, when they reboarded the vessel to recover personal effects, but the ship later went down by the bow. 24 men, including three survivors from the William Boyce Thompson were picked up by Jaguarão (CS 55) and landed at Fortaleza on 9 July. The 14 men in one of the remaining two lifeboats landed at Fortaleza on 9 July and the other boat made landfall at Cascavel, Brazil the same day.