The ships were designed by naval engineer William Reed, of Smith's Dock Company of South Bank-on-Tees, to have the endurance and anti-submarine capabilities of the Black Swan-class sloops, while being quick and cheap to build in civil dockyards using the machinery (e.g. reciprocating steam engines instead of turbines) and construction techniques pioneered in the building of the Flower-class corvettes.

After commissioning in December 1942, Itchen participated in anti-submarine warfare exercises off Tobermory, Mull and Lough Foyle until mid-September 1943 where she was assigned as convoy escort.

At 21:51 on 20 September, HMCS St. Croix took three hits from U-305 in the stern and sunk, with 81 survivors being picked up by Itchen.

During this, at 22:53 on 20 September, the German submarine U-305 fired a torpedo at Itchen but missed and HMS Polyanthus was sunk screening the rescue.

At 02:01 on the morning of 23 September, U-666 fired a torpedo at Itchen which hit the ship after 70 seconds.