SS Dettifoss was an Icelandic Cargo Ship that was Torpedoed by German submarine U-1064 in the Irish Sea 25 nautical miles (46 km) out of Belfast, United Kingdom (55°03′N 5°29′W / 55.050°N 5.483°W / 55.050; -5.483), while she was travelling from New York, United States to Belfast, United Kingdom and later to Reykjavík, Iceland.

When she was torpedoed by the German submarine U-1064 at 08.39 hours in the Irish Sea 25 nautical miles (46 km) out of Belfast.

Dettifoss sank within 7 minutes resulting in the death of 12 crew members and 3 passengers.

The 29 survivors (18 crew and 11 passengers) were picked up an hour after the sinking by HMS Fusilier (T305) and were then taken to Scotland and later to Iceland.

The sinking of Dettifoss was a harsh blow so soon after the loss of SS Godafoss.