At 22.53 hours on 20 September 1943, U-305 (Bahr) missed HMS Itchen (K 227) with a Gnat in 57°30N/31°10W, after sinking HMCS St. Croix (I 81) (LtCdr A.H. Dobson, DSC, RCNR) near convoy ON-202. At 04.35 hours on 21 September, U-270 (Otto) fired a Gnat in grid AK 2882 and heard an end-of-run detonation after 11 minutes. The target of the attack must have been HMS Itchen or HMS Narcissus (K 74) (Lt W.G.H. Bolton, RNR). At 23.57 hours on 22 September, U-952 (Curio) fired a Gnat in grid AK 7156 and heard an end-of-run detonation after 10 minutes 3 seconds. The target of this attack may have been HMS Itchen or FFL Renoncule (K 117).

At 01.56 hours on 23 September, U-666 fired a Gnat which detonated after 8 minutes 21 seconds in the wake of HMCS Morden (K 170) (T/Lt E.C. Smith, RCNVR). At 02.01 hours the U-boat fired another Gnat that struck HMS Itchen (K 227) (Cdr C.E. Bridgman, DSO, RNR) after 1 minute 10 seconds. The frigate blew up after the hit. Debris from the vessel was later found on the conning tower of the U-boat and on HMCS Morden. HMS Itchen had picked up 81 survivors from HMCS St. Croix and one from HMS Polyanthus (K 47) (Lt J.G. Aitken, RNR), which had been sunk by U-952 (Curio) on 21 September. Only two men from HMS Itchen and one from HMCS St. Croix were rescued by the Polish steam merchant Wisla.