At 06.26 hours on 12 Apr, 1942, U-203 (Mützelburg) fired a spread of three torpedoes at the Stanvac Melbourne (Master Andrew T. Lagan) and another steamer overlapping with the tanker (however, no other ship is mentioned in the Allied report) about 15 miles from Frying Shoal Inside Buoy in 33°53N/77°29W. The tanker was en route in ballast from New York to Aruba. One torpedo apparently detonated when it hit the bottom beneath the stern of the tanker, which stopped to be examined for damage and then continued seven minutes later without zigzagging. At 07.06 hours, the U-boat fired another torpedo in grid DC 1177 that struck on the port side at #7 tank and opened a 30ft to 30ft hole and several small holes on the starboard side, causing a list to port. The 40 crew members and eight armed guards abandoned ship in four lifeboats except the master, an oiler and an armed guard. One boat got troubles on launching and was finally released with only one man in it, while three men abandoned ship on rafts. One crewman went missing after abandoning ship.

The chief mate later reported that he saw two U-boats and one of them surfaced under their lifeboat and capsized it. The boat was later rightened but two men perished and were buried at sea. The remaining survivors in the boat were picked up 13 hours after the attack by the American submarine chaster USS PC-472, transferred to the US Coast Guard vessel CG-186 and landed at Southport, North Carolina on 14 April. The 14 survivors in a second lifeboat were picked up by the motor merchant William Penn and landed at Morehead City, North Carolina.
The three men on the tanker dropped the port anchor and hoped that the boats were able to return to the ship, but they stayed there all night. In the afternoon of 12 April, two tugs and the HMS Northern Duke (4.11) came to assist the tanker and took her in tow to Southport, arriving the next day. On 14 April, the tow proceeded for temporary repairs to Wilmington, North Carolina. On 16 April, the crew returned to their ship, which returned to service on 2 July after permanent repairs at Charleston, South Carolina. 

At 10.00 hours on 12 Sep, 1942, the unescorted Stanvac Melbourne (Master Andrew T. Lagan) was hit on the port side by two torpedoes from U-515 about 15 miles southeast of Emerald Shoals off Trinidad. The first torpedo struck just forward of the bridge and the second just aft of the bridge and developed a 25° list to port and kept headway until the engines were stopped. The 40 crew members and nine armed guards abandoned ship in three lifeboats, except the master, the second mate, the radio operator and a seaman. At 10.20 hours, a first coup de grâce missed, but a second hit four minutes later the engine room in the stern and blew holes in both sides of the vessel. The remaining men now abandoned ship by jumping overboard and were picked up by the boats. About one hour later, the tanker turned over and sank by the stern with her bow straight up. One crew member was lost.
At daybreak, the three lifeboats headed for Trinidads and that night made landfall near Toco Point, where they were met by natives and later taken to Port of Spain. On 16 September, the survivors were repatriated aboard a US Army transport.

The master Andrew T. Lagan survived both U-boat attacks on the Stanvac Melbourne, but died when his next ship, the Brilliant was torpedoed by U-43 (Schwantke) on 18 Nov, 1942.