'Lentil' was a British carrierborne air attack on the oil refinery at Pangkalan Brandan on Sumatra in the Japanese-occupied Netherlands East Indies as a second rehearsal for 'Meridian I' (4 January 1945).
On 22 November 1944 Admiral Sir Bruce Fraser’s Eastern Fleet had ceased to exist as the British prepared to make a major contribution to the Allied naval strength on the Pacific Ocean using many of the assets of the erstwhile Eastern Fleet. The part of the Eastern Fleet scheduled to remain in the area of Admiral the Lord Louis Mountbatten’s South-East Asia Command became the East Indies Fleet, led by Vice Admiral Sir Arthur Power and comprising the battleship Queen Elizabeth, the battle-cruiser Renown, eight cruisers, five escort carriers (including two ferry carriers), 24 destroyers, and escort forces totalling some 70 ships.
The other part of the erstwhile Eastern Fleet became the Pacific Fleet 1 under the command of Fraser, and on 2 December Fraser departed Ceylon in Howe for Australia, whence he was to fly to Pearl Harbor in the Hawaiian islands group to see Admiral Chester W. Nimitz, commanding the Pacific Ocean Areas, leaving the rest of his fleet to follow at a date to be decided later. He arranged, however, that before the ships of the Pacific Fleet left the Indian Ocean, Power would use them to carry out a series of operations designed to interfere with Japanese oil supplies as well as develop the differing tactical skills which would be required for operations against the Japanese.
Power selected as targets the oil refineries at Pladjoe and Soengei Gerong near Palembang, which were to be attacked in 'Meridian I'. As a rehearsal he ordered Vian to use Task Force 63 2 in an attack on the Japanese-operated refineries at Pangkalan Brandan, some 30 miles (48 km) to the north-west of Belawan Deli in northern Sumatra.
Vian’s force departed Trincomalee on 17 December and, without being detected, reached the designated flying-off position early on 20 December. Here, at 07.15, Vian launched 27 Grumman Avenger torpedo and level bombers escorted by 28 Grumman Hellcat and Vought Corsair fighter-bombers. Finding their target obscured by cloud, the aircraft attacked the port at Belawan Deli as an alternative, achieving only modest results as the target area was obscured by heavy squalls and low cloud. As the aircraft returned to their carriers, they attacked the airfields around Sabang, destroying several Japanese aircraft on the ground.
On 4 January 1945 Vian, with the carriers Indomitable, Victorious and Indefatigable, heavy cruiser Suffolk, light cruiser Ceylon, light anti-aircraft cruisers Argonaut and Black Prince, and eight destroyers, attacked Pangkalan Brandan in 'Lentil' and succeeded in causing considerable damage: the attack aircraft badly damaged the refinery, and the fighters shot down about 12 Japanese aircraft as well as destroying another 20 on the ground. The British lost only one aeroplane, an Avenger whose crew was rescued.
The British force then returned to Ceylon, and on 16 January Vian finally departed for the Pacific, where Fraser and Howe were already present, with his four fleet carriers, one battleship, three cruisers and 10 destroyers. Vian took the opportunity on 24 January, after a two-day postponement for weather reasons, to launch 'Meridian I' with 43 Avenger attack aircraft armed with 500-lb (227-kg) bombs and 12 Fairey Firefly attack aircraft armed with air-to-surface unguided rockets, escorted by about 50 fighters, against Pladjoe.