The SS Ajax was a Danish cargo ship that was torpedoed by U-104 in the Bay of Biscay off Audierne, France, while she was travelling from Bilbao, Spain, to Cardiff, Wales, United Kingdom.

She sailed under the name SS Antiquary under the British flag until she was sold in 1901 to Torm Dampskibselsskabet in Copenhagen, Denmark.

She had a triple expansion steam engine driving a single screw propeller.

On 25 December 1917, Ajax was on a voyage in a convoy from Bilbao, Spain, to Cardiff, Wales.

The ship sank to a depth of over 58 metres (190 ft), along with its cargo and the eleven sailors.