'Neptun' (i) was a U-boat wolfpack operation in the Atlantic against the HX.226 and HX.227 convoys (18 February/3 March 1943).

The wolfpack comprised U-89, U-135, U-359, U-376, U-377, U-405, U-448, U-566, U-608, U-634, U-659, U-709 and U-759, and for the loss of none of its own number sank two ships (14,352 tons) of the HX.227 convoy.

Initially comprising U-135, U-359, U-376, U-405, U-448, U-566, U-608, U-659 and U-759, the 'Neptun' (i) wolfpack was created in the area to the south-west of Iceland to intercept the HX.226 convoy, which was supported by Commander K. F. Adams’s Canadian Escort Group C3 (destroyers Assiniboine and British Burnham, British frigate Jed, and corvettes Bittersweet, Eyebright and La Malbaie). The convoy and its escort in fact passed to the north of the wolfpack on 20 February after being re-routed as a result of 'Ultra' intelligence.

When the convoy was not located, the pack, reinforced by U-89, U-569 and U-377, was instructed to move to the south-west in the direction of the SC.120 convoy, which was supported by Commander P. W. Gretton’s British Escort Group B7 (frigate Tay. destroyer Vidette, corvettes Alisma, Loosestrife, Pink and Snowflake, and temporarily attached sloop Woodpecker), and also the HX.227 convoy of 62 ships supported by Commander R. Heathcote’s British Escort Group B6 (destroyers Fame and Viscount, and corvettes Kingcup, Vervain and Norwegian Acanthus and Potentilla). Again, however, the convoys passed to the north of the wolfpack’s patrol line after being re-routed on 24/25 February.

The HX.227 convoy’s detour was not quite far enough to the north, however, and the convoy was located by U-759, the most northerly boat of the 'Neptun' (i) wolfpack, during the morning of 27 February, although radio interference then delayed the timely deployment of the wolfpack’s boats. U-759 was driven off by the escorts, but U-135, U-359, U-376, U-377, U-448 and U-608 followed. Only Korvettenkapitän Rolf-Heinrich Hopmann’s U-405 met with any success, though, sinking the 7,176-ton US Wade Hampton, which had started to straggle and was carrying as cargo two PT-boats destined for the USSR.

From 28 February U-634 and U-709 also joined the wolfpack.

On 1 March U-759 shadowed and reported the straggling 7,176-ton US Meriwether Lewis, which Oberleutnant Eberhard Dahlhaus’s U-634 sank. During the afternoon U-608 sighted and reported ON.168 convoy supported by Commander R. C. Boyle’s British Escort Group B5 (destroyers Havelock and Volunteer, frigate Swale, and corvettes Buttercup, Godetia, Lavender, Pimpernel and Saxifrage), just to the north, but the HF/DF-equipped Havelock heard and fixed the reporting signal, arrived at the scene and forced the U-boat to submerge, and contact was thereupon lost.