'Hammer' (iv) was a U-boat wolfpack operation against the JW.58 convoy during its 'FY'-supported passage to the northern USSR (10 March/5 April 1944).

The wolfpack comprised U-288, U-354, U-674, U-968 and U-990, and for the loss of Oberleutnant Willy Meyer’s U-288 on 3 April, to an attack of a Fairey Swordfish attack aeroplane of No. 819 Squadron from the escort carrier Activity and a Grumman Wildcat and a Grumman Avenger of No. 846 Squadron from the escort carrier Tracker, sank no ship.