'DU' (i) was a British naval sweep into the Skagerrak in search of German shipping for interception and destruction (19/24 March 1940).

At 15.00 on 19 March the battleships Rodney, Valiant and Warspite, supported by the destroyers Hardy, Hasty, Hero, Hostile, Hotspur, Hunter and Hyperion of the 2^nd Destroyer Flotilla, and Fearless and Forester of the 8^th Destroyer Flotilla, departed Scapa Flow in the Orkney islands group to cover the movements of the HN.20 and ON.21 convoys, and also to undertake 'DU' (i). At the same time and for the same purpose, the battle-cruisers Renown and Repulse, supported by the destroyers Delight, Diana, Ilex and Inglefield of the 3^rd Destroyer Flotilla, Bedouin of the 6^th Destroyer Flotilla and Fortune of the 8^th Destroyer Flotilla, departed Scapa Flow.

'DU' (i) proper began at 23.30 on 20 March as the light cruisers Arethusa, Aurora, Galatea and Penelope of the 2^nd Cruiser Squadron departed Scapa Flow with the destroyers Fame, Firedrake, Foresight, Foxhound, Mashona, Matabele, Sikh and Somali in two groups. The 8,096-ton German merchant vessel Neuenfels was challenged by two of the 'DU' (i) undertaking’s destroyers near Lindesnes, but escaped into the Rosfjord.