'Seeteufel' was a U-boat wolfpack operation in the Atlantic primarily against the ONS.1 convoy (21/30 March 1943).

Eight boats formed the pack on 21 March, and another seven joined it after this date to create a wolfpack which thus came to comprise U-91, U-134, U-169, U-188, U-260, U-306, U-415, U-469, U-526, U-564, U-572, U-592, U-610, U-632, U-663 and U-706, and for the loss of Oberleutnant Hermann Bauer’s U-169 and Oberleutnant Emil Claussen’s U-469 sank one 7,176-ton ship of the HX.230 convoy.

The wolfpack was established in the area to the south of Iceland with U-188, U-260, U-306, U-415, U-564, U-572, U-592 and U-663 to operate against the ONS.1 convoy, which was the first of a new series following the ONS.171 convoy, last of the previous series. The new convoy was located by the B-Dienst naval signals intercept and decryption service, and over the following days U-91, U-134, U-523, U-526, U-610, U-632 and U-706 joined the wolfpack.

On 24 March U-306 sighted escorts of the ONS.1 convoy, which was supported by Lieutenant Commander R. Heathcote’s British Escort Group B6 (destroyers Fame and Viscount, and corvettes Kingcup, Vervain and Free Norwegian Acanthus and Eglantine) in the area to the north of the wolfpack, but the four most northerly boats and U-168, proceeding from the Denmark Strait, did not come up.

From 25 March the 'Seewolf' (ii) wolfpack (U-84, U-86, U-257, U-305, U-333, U-336, U-373, U-440, U-441, U-591, U-527, U-530, U-590, U-615, U-618, U-631, U-641, U-642 and U-666) was formed in the area to the south of the 'Seeteufel' wolfpack to intercept the SC.123 convoy, which had also been located by the B-Dienst. On their way to join these wolfpacks, U-469 and U-169 were sunk, on 25 and 27 March respectively, by a Boeing Fortress long-range patrol bomber (flown by different crews) of the RAF’s No. 206 Squadron.

In the afternoon of 26 March U-564 sighted the SC.123 convoy, which was supported by Commander D. G. F. W. MacIntyre’s British Escort Group B2 (sloop Whimbrel, destroyers Vanessa and Whitehall, and corvettes Clematis, Gentian, Heather and Sweetbriar), but wrongly reported that the convoy was proceeding to the west. The 'Seeteufel' wolfpack was ordered to close the convoy, and U-415 and U-663 gained brief contact, but the escort group had meanwhile been reinforced by the Captain Giles E. Short’s US 6^th Escort Group (escort carrier Bogue and destroyers Belknap and George E. Badger), and carrierborne aircraft forced the boats to submerge.

On 27 March U-305, which was the most northern of the boats, sighted the following HX.230 convoy, which had been re-routed to the north, and this comprised 45 ships supported by Commander E. C. Bayldon’s British Escort Group B1 (destroyers Hurricane, Rockingham and Watchman, frigate Kale, and corvettes Dahlia, Meadowsweet, Monkshood and Wallflower) reinforced by Captain J. A. McCoy’s 3^rd Support Group (destroyers Offa, Obedient, Oribi, Orwell, Onslaught and Icarus).

Of the 22 'Seewolf' (ii) and 'Seeteufel' boats deployed, only U-305, U-631, U-591, U-415 and U-610 managed to approach the convoy for a time, the last sinking the 7,176-ton US William Pierce Frye. The wolfpacks were impeded by a south-westerly gale and several times driven off by the strong air escort again without gaining any other success, and on 30 March U-631 was the last boat to lose contact, whereupon the operation was broken off.