'Hai I' was a U-boat wolfpack operation in the Atlantic against the HX.278 and ON.224 convoys (17/22 February 1944).

The wolfpack comprised U-91, U-212, U-256, U-264, U-386, U-406, U-437, U-441, U-546, U-549, U-603, U-608, U-709, U-764, U-985 and U-989, and for the loss of Kapitänleutnant Hartwig Looks’s U-264, Oberleutnant Fritz Albrecht’s U-386 and Kapitänleutnant Horst Dieterichs’s U-406 sank only the British sloop Woodpecker escorting the ON.224 convoy.

On 16 February the HX.278 convoy, supported by Commander D. G. F. W. MacIntyre’s Escort Group B2, Commander P. W. Gretton’s Escort Group B7, Captain F. J. Walker’s 2^nd Support Group (sloops Starling, Kite, Magpie, Wild Goose and Woodpecker) and Commander G. A. G. Ormsby’s 10^th Support Group (frigates Spey, Findhorn, Lossie and Rother), approached the German U-boat patrol line from the south-west. U-546 and U-984 were able to beat off the night attacks of radar- and Leigh Light-equipped British maritime aircraft with their 37-mm anti-aircraft guns, but could not attack the convoy.

On 17 February, after the HX.277 convoy had passed the U-boat patrol line, Admiral Sir Max Horton, the commander-in-chief Western Approaches, despatched the 2^nd Support Group and Escort Group B7 to aid the ON.224 convoy, and the 10^th Support Group to aid the ONS.29 convoy that, together with the escort carrier Striker, was located and reported in the afternoon by a Junkers Ju 290 long-range maritime reconnaissance aeroplane.

Grossadmiral Karl Dönitz, still in operational control of the U-boat arm in addition to being the commander-in-chief of the German navy, ordered the establishment of the 'Hai I' wolfpack to tackle these convoys. The wolfpack was detected by the British, however, and the convoy was therefore rerouted to pass round the wolfpack’s southern end. Dönitz sought to counter this bypass undertaking, which had been detected by the radio intercepts and decrypts of the B-Dienst, by ordering the despatch of no fewer than 10 reconnaissance aircraft, three of which located the convoy; one of these three was shot down by British fighters. During the night of 18/19 February the convoys passed the U-boat patrol lines and, in the process, on 18 June Spey sank U-406, whose survivors included several radar experts, and on 19 June U-386.

On 19 February Woodpecker and Starling sank U-264, which was the first Schnorchel-fitted U-boat, and U-437 and U-764 missed the escorts with several torpedoes, though U-256 did torpedo the sloop Woodpecker, which sank while under tow on 27 February.

Stationed on its own off the Scilly Isles, U-413 sank the destroyer Warwick on 20 February.