She had a dive time of 48 seconds and was capable of operating at a depth of 50 metres (160 ft).

This in turn resulted in the forward compartment flooding, the batteries failing, and chlorine gas developing.

[7] A 12-pdr shell from the Sylvia hit the submarine's conning tower, killing her commander, Horst Ruhle von Lilienstern, and a second shell hit the hull and she began to sink, after which two depth charges were dropped right beside the UC-55, resulting in the U-boat blowing up.

The Moravia then closed with the wreck, fired two more shots into her, and dropped a final depth charge.

[8] The wreck of UC-55 was discovered by side scan sonar lying on its keel on 3 July 1985, at a depth of 105 m (344 ft) at 60°3′13″N 0°57′57″W / 60.05361°N 0.96583°W / 60.05361; -0.96583.