'SF' was a British naval and air operation against U-boats making the outbound and inbound passages through the Iceland/Færoes passage (5 August 1943 onward).

The undertaking was controlled by Admiral Sir Wilbraham Ford, the commander-in-chief Rosyth, to facilitate co-operation with Air Vice Marshal A. B. Ellwood’s No. 18 Group of Air Marshal Sir John Slessor’s RAF Coastal Command. The operation took the form of sweeps by a force of three destroyers of Admiral Sir Bruce Fraser’s Home Fleet, in this instance from a forward base in the Skálafjørður of the Færoe islands group, supported by aircraft of No. 18 Group.

Under the command of Captain J. A. McCoy (from 12 July Commander J. Lee-Barber), the destroyers Onslow (from 12 July Opportune), Obdurate and Orwell escorted a tanker to the Skálafjørður and began their sweeps on 5 July. The operation’s first fortnight proved fruitless, and as a result of the pressure of other operations, the shortage of destroyers and the scarcity of U-boats, 'SF' was temporarily suspended on 17 July and the destroyers and their supporting oiler returned to Scapa Flow. So that 'SF' could be resumed, on 27 July the oiler Blue Ranger was despatched to the Skálafjørður under escort of the destroyers Oribi and Orwell. These two destroyers constituted Group 'A', which resumed 'SF' on 29 July and were supplemented from the following day by the destroyers Mahratta, Milne and Musketeer as Group 'B'. The operation continued throughout August, when Oberleutnant Adalbert Schmandt’s U-489 was sunk by a Short Sunderland flying boat of Coastal Command, assisted by the destroyer Castleton, on 4 August. In making its attack the Sunderland was itself shot down, the destroyers Castleton and Orwell recovering the flying boat’s survivors as well as those of the U-boat, which included the crew of the fifth Blohm und Voss Bv 138 flying boat shot down in 'Governor'.

During August the destroyers involved in 'SF' were Beaumaris, Bootle, Castleton, Dunbar, Fraserburgh, Llandudno, Mahratta, Matchless, Meteor, Musketeer, Onslow, Oribi, Orwell, Sabre, Sardonyx, Shikari, St Mary’s, Ulster, Wells and Worthing. The operation continued into September and later, and during the earliest of these months the destroyers were complemented by minesweepers, and the ships involved during the month were the destroyers Impulsive, Mahratta, Meteor, Middleton, Obedient, Onslow, Oribi, Sabre, Sardonyx, Savage, Scorpion, Scourge and Shikari, and the minesweepers Ardrossan, Beaumaris, Bootle, Dunbar, Fraserburgh, Gleaner, Harrier, Hussar, Llandudno, Lyme Regis, Salamander and Worthing.

In October the destroyers were Savage, Sardonyx, Scorpion and Scourge, and the minesweepers Ardrossan, Bootle, Fraserburgh, Gleaner, Harrier, Hussar, Llandudno, Lyme Regis, Salamander and Worthing.

'SF' continued throughout November, as in the previous month on a reduced scale as no destroyers were available and as the 15^th Minesweeping Flotilla was being replaced at the Skálafjørður in the Færoe islands group during the middle part of the month by the 18^th Minesweeping Flotilla, and the 1^st Minesweeping Flotilla was fully occupied with Arctic convoy work. The November patrol took place without incident from the Seyðisfjörður in eastern Iceland as well as the Skálafjørður, and the minesweepers involved were Ardrossan, Bootle, Cockatrice, Fraserburgh, Hound, Hydra, Llandudno, Lyme Regis, Orestes, Rattlesnake, Ready and Worthing.

The scale of 'SF' was still further reduced in December as a result of the minesweepers' considerable commitment in other tasks. The 18^th Minesweeping Flotilla carried out two patrols at the beginning of the month, but otherwise the ships remained at Skálafjørður. The minesweepers involved were Cockatrice, Hound, Hydra, Loyalist, Orestes and Rattlesnake. As a result of the demand for minesweepers to serve as local escorts for north Russian convoys and in special operations exercises, there were no minesweepers available for 'SF' in February 1944 until the last day of the month when Cockatrice, Hydra, Onyx and Orestes undertook a four-day patrol before being required for the local escort of the RA.57 convoy.