'IS1' was a British naval gunfire bombardment of Tobruk on the coast of Italian Libya (17/21 January 1940).

Tobruk was bombarded on the nights of 18/19 and 19/20 January by the monitor Terror and the gunboat Aphis operating from Alexandria, from which they had departed on 17 January. On 18 January the light cruiser Orion and the light anti-aircraft cruiser Bonaventure departed Alexandria with the destroyers Hero, Jervis and Nubian to support 'IS1', the cruisers operating to the north-east of Tobruk and the destroyers to the target’s west. On the night of 20/21 January Terror and the gunboats Gnat and Ladybird bombarded Italian positions at Marsa el Shal near Tobruk.