On the 11th March 1941 SS Britannia set out from Liverpool to Freetown, Durban and Bombay.

She was originally a passenger ship of the Anchor Line and was operating as a troop ship under the command of Captain Alexander Collie.

The voyage began with the Britannia as a member of a convoy with an anti-submarine escort. By the 25th of March the rest of the convoy had disappeared and the Britannia was on her own. Early that same morning she was attacked by the German Hilfskreuzer (auxiliary cruiser) Thor, also a converted merchant ship, under the command of Kapitän Otto Kähler.

The Thor was armed with six 5.9 inch guns and easily overpowered the Britannia. When her single rear 4 inch gun was destroyed Captain Collie gave the order to abandon ship.

Britannia's radio operator had managed to get off an RRR (Raider, Raider, Raider) signal with her location, which was acknowledged by Sierra Leone radio. The Thor picked up radio traffic which indicated that a Royal Navy warship was on its way at speed. In the light of this information, Kapitän Kähler did not stay to pick up survivors.

After giving warning and allowing time to abandon ship, he shelled the Britannia on her waterline and she sank quickly. He heard later that no warship had arrived and that some of the survivors had spent many days on rafts and in lifeboats before being picked up by other ships that happened to be in the area.