'OB' (i) was a British naval operation to provide air cover for the shipping and troops at Narvik during the Norwegian campaign (11/18 May 1940).
On 11 May, the fleet carrier Ark Royal provided fighter patrols over arriving British ships together with light anti-aircraft cruiser Curlew and the destroyers Encounter, Inglefield, Jaguar and Mashona. On the same day three light cruisers were operating off northern Norway, Penelope escorting a convoy off Narvik, Aurora patrolling off Narvik, and Enterprise escorting the convoy bringing a force of Scots Guards to Mo. In this last undertaking, Enterprise was supported by the light anti-aircraft cruiser Cairo, destroyer Hesperus and sloop Fleetwood. The warships departed Narvik with 4,545-ton store ship Margot, which was carrying four field guns and a light anti-aircraft battery, and Enterprise landed 320 men at Mo during the night and also supported other troops already ashore.
On 12 May, Ark Royal launched two flights of Blackburn Skua warplanes of No. 800 Squadron: one of these headed toward Penelope and her convoy, and the other toward Mo to cover the landing of the Scots Guards.
On 13 May Ark Royal continued in the same basic task, and the battleship Resolution, heavy cruiser Effingham, light cruiser Aurora, repair ship Vindictive, netlayer Protector, and destroyers Basilisk, Fame, Havelock, Somali and Wren (9th Destroyer Flotilla) were dispersed from Bjerkvik, Effingham to proceed to Harstad. Resolution, Effingham, Vindictive, Basilisk, Fame, Havelock, Somali and Wren shelled the German positions in Narvik, assisted by aircraft from Ark Royal.
The carrier continued to fly off fighter patrols over the Narvik area up to 18 May.