| Operation Mo | |
|---|---|
 | |
| Planned | April 1942 |
| Objective | Occupation of Port Moresby |
| Outcome | Abandoned following theBattle of the Coral Sea |
Operation Mo (MO作戦,Mo Sakusen) or thePort Moresby Operation was aJapanese plan to take control of the AustralianTerritory of New Guinea duringWorld War II as well as other locations in theSouth Pacific. The goal was to isolateAustralia andNew Zealand from theAlliedUnited States.
The plan was developed by theImperial Japanese Navy and supported by AdmiralIsoroku Yamamoto, the commander-in-chief of theCombined Fleet, but the operation was eventually abandoned.
When the Japanese Navy was planning theNew Guinea Campaign (air strikes againstLae andSalamaua, disembarkation inHuon Gulf, New Britain (Rabaul), New Ireland (Kavieng),Finch Harbor (also called Finschhafen), and the capture ofMorobe andBuna), strategists envisioned those territories as support points to implement the capture ofPort Moresby. The implementation of these operations was assigned to the Japanese Naval task force led byAdmiralChūichi Nagumo, after completing theJava campaign. Another important step was the occupation ofChristmas Island to the south of Java. The Japanese Navy General Staff had been considering Operation Mo since 1938, as a step in the consolidation of the Southern Seas areas in theGreater East Asia Co-Prosperity Sphere (大東亜共栄圏,Dai-tō-a Kyōeiken).[citation needed]
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The Directive of Operation Mo was conceived in 1938, but with no specific time for its execution, pending earlier successes in the southern area during the first and second phases of the conquest.
In April 1942, the operation was organized into four large actions and was approved by the Army and Navy General Staffs:
Japanese planners took into account an Allied response to the operation by detaching one task force to the west of parallel between ofRennel andDeboyne Islands and another to the east of same point. These measures would permit a Japanese invasion force to use theJomard Passage directly to Port Moresby. Japanese naval intelligence also suspected the presence of the Americanaircraft carrierUSS Yorktown inCoral Sea waters during this period.
A Japanese message on 9 April 1942 indicated that the "RZP Campaign" against Port Moresby was to be an invasion, not an air raid, and which would isolate Australia from America. USN codebreaker Rudy Fabian atFRUMEL briefed MacArthur who was "incredulous" as he expected the target would be New Caledonia, so Fabian explained the (JN-25) code-breaking process and showed him the Japanese commander’s intercepted message with the objectives to restrict enemy fleet movements and attack the north coast of Australia. So a transport due to leave the next day for New Caledonia was sent to Port Moresby. On 23 April Fabian showed MacArthur that the IJN was amassing a large force at Truk, and planned to occupy Tulagi also. MacArthur got an Australian reconnaissance plane to "discover" the Port Moresby invasion force on 5 May, leading to theBattle of the Coral Sea (seeCentral Bureau).[1]
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The Tulagi assault force, led by Rear AdmiralKiyohide Shima, was composed of the following units:
The Port Moresby occupation force, led by Rear AdmiralSadamichi Kajioka, was composed of the following units:
Supporting these operations and intercepting any Allied interference, Rear AdmiralAritomo Goto commanded:
During the course of operation,Yamamoto sent the following heavy support force fromTruk, led by Rear AdmiralChuichi Hara:
Supporting this force was the 25th Air Fleet, (Yokohama Air Corps) led by Rear AdmiralSadayoshi Yamada, based in Rabaul,Lae,Salamaua,Buna andDeboyne Islands, composed of 60Mitsubishi A6M "Zero" fighters, 48Mitsubishi G3M "Nell" and 26Aichi E13A "Jake" andMitsubishi F1M "Pete" reconnaissance seaplanes. This unit bombed Port Moresby on 5–6 May, ahead of the Japanese Army-Navy landing on 7 May.
The Tulagi assault forcebegan their landings on Tulagi on 3 May. On 4 May 1942, troopships bearing theSouth Seas Detachment set sail southward from Rabaul for Port Moresby. This same day US aircraft fromYorktown attacked the Tulagi assault force, inflicting heavy damage, but were unsuccessful in preventing theoccupation of Tulagi, Gavutu, and Tanambogo islands.
Three days later, as a naval engagement appeared to be brewing in theCoral Sea, the Japanese Moresby transports immediately veered back to the north, in order to avoid combat. The resultingBattle of the Coral Sea inflicted significant aircraft losses on theFourth Fleet,Shōhō was sunk, andShōkaku was damaged. Air groups from the two carriers, including the relatively undamagedZuikaku, suffered such sizable losses, it was necessary they return to Japan to re-equip and train.
The Japanese abandoned their plans to land the South Seas Detachment directly at Port Moresby from the sea. The Japanese Army was making new preparations for combat when, on 11 July, High Command ordered the suspension ofOperation FS the projected actions againstNew Caledonia,Fiji, andSamoa, after the remaining Japanese carrier strength was destroyed at theBattle of Midway.
These battles prevented the Japanese landings against Port Moresby. Instead the Japanese army commenced an ultimately unsuccessful campaign to take Port Moresby with an overland approach across theOwen Stanley Range via theKokoda Track.