| Conflict: | Operation Stab |
| Partof: | the Pacific Theatre of the Second World War |
| Map showing the Andaman Islands in the Indian Ocean | |
| Place: | Bay of Bengal, Indian Ocean |
| Coordinates: | 15°N 88°W |
| Date: | 21 July 1942 – 4 August 1942 |
| Result: | Allied success |
| Combatant1: |  United Kingdom Australia |
| Combatant2: | Japan |
| Commander1: | James Somerville |
| Commander2: | Unknown |
| Units1: | 1 battleship 2 carriers 4 light cruisers 6 destroyers 1 minelayer 2 corvettes 2 sloops 1 aux vessel 2 tankers 10 transport ships |
| Units2: | Unknown |
| Casualties1: | 4 aircraft destroyed 4 killed (flying accidents) |
| Casualties2: | 1 aircraft destroyed 9 killed |
Operation Stab was a British naval deception during the Second World War to distract Japanese units for the forthcoming Guadalcanal campaign by the US armed forces.
Admiral Ernest King, the head of the US Navy, to provide a distraction for the forthcoming Guadalcanal Campaign. The Admiralty discussed the request with Vice-Admiral Sir James Somerville, the Commander-in-Chief of the Eastern Fleet, stressing their apprehension at sending aircraft carriers into areas where they could be attacked by land-based aircraft. Operation Pedestal, a convoy operation to Malta, was due in early August, in which two aircraft carriers were to sail into range of Luftwaffe and Regia Aeronautica airfields and wanted to wait to discover their fate.
The Admiralty view limited the scope of a diversion operation to air attacks on Port Blair in the Andaman Islands or Sabang in northern Sumatra. The Dutch naval commander, Vice-Admiral Conrad Helfrich suggested that a raid on Sabang was pointless as the jungle made easy the dispersal and camouflage of aircraft. The main target in an attack on Port Blair would be the Japanese flying boats based there which needed a fighter attack but the relatively short range of these aircraft would mean that their aircraft carriers would be risking attack by land-based aircraft. A deception operation against the Andaman Islands, which had been captured by the Japanese in March 1942, was chosen instead.
Three dummy convoys, Force V, consisting of, and, escorted by and would sail from Vizagapatam. Force M, from Madras, consisted of,,, and escorted by the fleet minelayer, the corvette and the auxiliary patrol vessel . Force T, from Trincomalee, consisted of the Royal Fleet Auxiliary tankers and with the freighters and escorted by the sloop and the corvette . The three convoys were to sail in daylight on 1 August and turn back to their ports during the night.
Somerville was to sail to the east of the convoys with Force A, based at Ceylon, consisting of the battleship, the aircraft carriers and, the light cruisers,, and the Netherlander, with the destroyers,,, and . Wireless messages were to be used to make sure that the Japanese discovered the ship movements and then to suggest that the operation has been postponed due to an accident.
On 28 July the Dutch submarine, in the Malacca Strait, reported two Japanese heavy cruisers and four destroyers at 5° 32' N, 98° 50' E, moving up the west coast of Thailand. Force V, which had no air cover was cancelled. Somerville judged that the force was a raid on Allied ships in the north of the Bay of Bengal, following the rumours planted in India of preparations for an attack on the Andaman Islands. Force M and Force T sailed on 1 August. After the report by O 23, Force A had sailed from Colombo on 30 July, conducted air reconnaissance and found nothing.
Force A was spotted by a Japanese flying boat at on 1 August and reports were picked up from Tokyo announcing the discovery. Late in the morning of 2 August another flying boat was shot down by a Martlet fighter from Formidable at 9° 26' N, 83° 16' E. Force A returned to Trincomalee late on 2 August as some of the ships were due to participate in Operation Stream, Operation Line and Operation Jane in the Battle of Madagascar. A wireless deception was undertaken to pretend that Force A was in the Bay of Bengal until 18 August.
While the operation was carried out without loss, the Japanese failed to take the bait and no significant naval or air units were redeployed – although the seaplane tender Sagara Maru was sent to the islands on 4 August and a bomber unit was sent to reinforce Sabang, it could be said to have been a minor success.[1]
Several Japanese aircraft were spotted and a Kawanishi H6K (Mavis) was shot down at 9° 26' N, 83° 16' E by a Martlet from Formidable. Two Martlets and two Fulmars were lost to accidents and engine failure.[2]