She was detailed to carry out a mail transfer with HMS Mermaid, a considerably larger ship at five times the displacement, 80 miles (130 km) north of the island of Texel.

Fittleton was caught in a low pressure area that exists near to the hull of a ship under way and was drawn close to the frigate HMS Mermaid by hydrodynamic forces.

A minor collision ensued and the Fittleton moved forward to try and exit the situation but instead was hit amidships by the bow of the much larger Mermaid and turned over within a minute.

[1] The following day, 21 September 1976, a marine crane, Magnus[1] lifted the wreck of the Fittleton from the seabed and the ship was taken to Den Helder in the Netherlands where she was made watertight.

Fittleton's crew had been paid just an hour before the sinking, with seamen receiving £50 or £87 depending upon rank, and large amounts of sodden money were scattered around the wreck when it was raised.