Operation Stab
Part of thePacific War of theSecond World War
The Bay of Bengal and the Andaman Sea
Date 21 July – 4 August 1942 Location Bay of Bengal,Indian Ocean 15°N88°E / 15°N 88°E /15; 88 Result Allied success
Belligerents
United Kingdom Australia  Netherlands	Japan
Commanders and leaders
James Somerville
Units involved
1 battleship 2 aircraft carriers 4 light cruisers 6 destroyers 1 minelayer 2 corvettes 2 sloops 1 auxiliary vessel 2 tankers 10 transport ships
Casualties and losses
4 aircraft destroyed 4 killed (flying accidents)	1 aircraft destroyed 9 killed
class=notpageimage| Location within Indian Ocean

Operation Stab was a British naval deception during theSecond World War to distract Japanese units for the forthcomingGuadalcanal campaign by the US armed forces.

AdmiralErnest King, the head of theUS Navy, asked for a distraction for the forthcoming Guadalcanal Campaign. TheAdmiralty discussed the request with Vice-Admiral SirJames Somerville, the Commander-in-Chief of theEastern 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 ofLuftwaffe andRegia Aeronautica airfields and wanted to wait to discover their fate.^[1]

The Admiralty view limited the scope of a diversion operation to air attacks onPort Blair in theAndaman Islands orSabang in northern Sumatra. The Dutch naval commander, Vice-AdmiralConrad 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.^[1]

Three dummy convoys, Force V, consisting ofBlackheath,Cranfield andMahout, escorted byHMIS Jumma andHMS Scout would sail fromVizagapatam. Force M, fromMadras, consisted ofTasmania,Hoperange,Clan McIver,Yuen Sang andCustodian escorted by the fleet minelayerHMS Manxman, the corvetteAster and the auxiliary patrol vesselSonovati. Force T, fromTrincomalee, consisted of theRoyal Fleet Auxiliary tankersRFA Appleleaf andRFA Broomdale with the freightersShenking andMarit Mærsk escorted by the sloopHMIS Hindustan and the corvetteHMS Marguerite.^[2] The three convoys were to sail in daylight on 1 August and turn back to their ports during the night.^[3]

Somerville was to sail to the east of the convoys with Force A, based atCeylon, consisting of the battleshipHMS Warspite, the aircraft carriersHMS Illustrious andFormidable, the light cruisersHMS Birmingham,Effingham,Mauritius and the NetherlanderHNLMS Jacob van Heemskerck, with the destroyersHMS Inconstant,HMAS Napier,Nizam,Norman andHNLMS Van Galen.^[4] 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.^[1]

On 28 July the Dutch submarineHNLMS O 23, in theMalacca 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 byO 23, Force A had sailed from Colombo on 30 July, conducted air reconnaissance and found nothing.^[5]

Force A was spotted by a Japanese flying boat at10:40 a.m. 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 fromFormidable 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 theBattle of Madagascar. A wireless deception was undertaken to pretend that Force A was in the Bay of Bengal until 18 August.^[5]

While the operation was carried out with no combat losses, the Japanese failed to take the bait and no significant naval or air units were redeployed – although the seaplane tenderSagara 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.^[6][7]

Several Japanese aircraft were spotted and aKawanishi H6K (Mavis) was shot down at 9° 26' N, 83° 16' E by aMartlet fromFormidable.^[8] Two Martlets and twoFulmars were lost to accidents and engine failure.^[9][6]

• Gray, Edwyn (1990).Operation Pacific. Annapolis, MD: Naval Institute Press. p. 137.ISBN 978-1-55750-650-4 – via Archive Foundation.
• Rohwer, Jürgen; Hümmelchen, Gerhard (2005) [1972].Chronology of the War at Sea, 1939–1945: The Naval History of World War Two (3rd rev. ed.). London: Chatham Publishing.ISBN 1-86176-257-7.
• Roskill, S. W. (1956).The Period of Balance.History of the Second World War United Kingdom Military Series: The War at Sea 1939–1945. Vol. II. London:HMSO.OCLC 174453986 – via Hyperwar Foundation.

• Battles of World War II involving Japan
• Guadalcanal Campaign
• Campaigns, operations and battles of World War II involving the United Kingdom
• Battles of World War II involving Australia

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