'MB3' was a British naval undertaking by Admiral Sir Andrew Cunningham’s Mediterranean Fleet in collaboration with the 'Hats' operation of Vice Admiral Sir James Somerville’s Gibraltar-based Force 'H' (30 August/5 September 1941).

On 30 August the Mediterranean Fleet’s Force 'I' departed Alexandria to provide distant cover for the MF.2 fast convoy (10,065-ton British Cornwall, 1,587-ton British Volo, 5,901-ton British auxiliary fleet oiler Plumleaf and 9,929-ton British commissioned transport Glengyle, escorted by only four destroyers in an attempt to lure the Italian fleet into an attack) from Alexandria to Malta and then to meet Force 'F' (battleship Valiant, fleet carrier Illustrious, light anti-aircraft cruisers Carlisle and Coventry, and destroyers Gallant, Greyhound, Griffin and Hotspur), which were traversing the length of the Mediterranean from Gibraltar to join the Mediterranean Fleet.

The movement of Force 'F' was supported by Force 'H' to the area of Malta, where responsibility devolved onto Force 'I', which was reinforced on 31 August by ships returning from a sweep into the Aegean Sea and then comprised the battleships Malaya and Warspite, the fleet carrier Eagle, the heavy cruiser Kent, the light cruisers Gloucester, Liverpool, Orion and Australian Sydney, and the destroyers Decoy, Defender, Hasty, Hereward, Hyperion, Ilex, Imperial, Australian Stuart, Vampire, Vendetta and Voyager, and Free Polish Garland.

On the following day Force 'I' came under air attack, and aircraft of Eagle spotted and reported major units of the Italian navy, which then turned back to base. On 2 September Force 'F' and Force 'I' met off Malta, and the now-reinforced Mediterranean Fleet headed to the east once again. Further sightings of Italian major warships were made, and on 4 September the British ships came under air attack, which delayed the launch of aircraft for the planned bombing of the airfield at Maritza on the Italian-held island of Rhodes, in which Eagle lost four aircraft.

The MF.2 convoy reached Malta on 2 September, and on 5 September the ships of the Mediterranean Fleet regained Alexandria.