Between 02.27 and 03.35 hours on 7 May 1942 the unescorted and unarmed Ontario (Master Anders Weesgaard) was shelled by U-507, while steaming a zigzag course at 12 knots. The day earlier, the ship was ordered to proceed to the nearest port after receiving a distress signal from the Alcoa Puritan, which was attacked and sunk by the same U-boat. U-507 attacked from the port quarter and destroyed the bridge, wheelhouse and the mainmast, after a distress signal was sent and soon left the burning and sinking vessel.
All 32 Americans, 11 Hondurians, one Dane and one British of the crew abandoned ship in three lifeboats and were picked up after six hours by the American patrol yacht USS Onyx (PYc 5) and landed at Burwood, Louisiana. The burning ship was last seen at 04.40 hours and a salvage crew returned later, but apparently she was gone down.

The master Anders Weesgaard survived this sinking, but died when his next ship the San Blas was sunk by U-158 (Rostin) on 17 June 1942.