The New Guinea campaign of the Pacific War lasted from January 1942 until the end of the war in August 1945.
During the initial phase in early 1942, the Empire of Japan invaded the Australian-administered territories of the New Guinea Mandate (23 January) and Papua (8 March) and overran western New Guinea (beginning 29/30 March), which was a part of the Netherlands East Indies. During the second phase, lasting from late 1942 until the Japanese surrender, the Allies consisting primarily of Australian and US forces cleared the Japanese first from Papua, then the Mandate and finally from the Dutch colony.

After a period of slow advances over the Owen Stanley Mountains in New Guinea, in which U.S. and Australian forces made limited gains at a cost of heavy casualties, the commander of the Southwest Pacific Theater, General Douglas MacArthur, in mid-1944 launched a daring series of amphibious landings behind Japanese lines to capture enemy bases on the north coast of New Guinea.

MacArthur was supported in his decisions by decrypts of Japanese communications that revealed accurate data about enemy strength and deployments. As the battle was being fought, decrypts about movements of enemy reinforcements forward allowed General George Kenney, MacArthur’s air officer, to prevent them from intervening in the battle.

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COL. Abraham Sinkov

The decrypts for planning were produced by Central Bureau (CB), a combined U.S. and Australian Cryptologic organization. The commander of CB was Colonel Abraham Sinkov, one of William Friedman’s original staff, now in uniform.

As the struggle to control New Guinea continued, CB consistently provided high-quality communication intelligence (COMINT) to MacArthur and Kenney about the Japanese troop numbers, status, and supply situation. Tactical intercept also was vital to decision making.

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GEN. Hatazo Adachi,
Commanding General of the Japanese 18th Army.

A decrypt of a Japanese message sent on May 28 revealed Japanese plans for a counterattack on American position in the coastal city Aitape. The Japanese 18th Army listed the supplies it needed for the attack and said that they had to arrive at the port of Wewak by the end of June. A message of June 20 said that the attack was to begin about 10 July, with a strength of 20,000 Japanese troops. This message also explained the deployment of each enemy division in the attack.

 

 

The attack happened as described, but the Americans were ready for it. The decrypt of an after action report from the Japanese commander showed that most Japanese artillery had been destroyed and a large number of troops lost. The supply situation was dire:  the commander illustrated this by saying the men had made ten-days’ ration of rice last twenty five days by eating it raw instead of cooking it.

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Troops unloading supplies at Aitape.  In the background are the
two AK’s.

The campaign resulted in a crushing defeat and very heavy losses for Empire of Japan. As in most Pacific War campaigns, disease and starvation claimed more Japanese lives than enemy action. Most Japanese troops never even came into contact with Allied forces, and were instead simply cut off and subjected to an effective blockade by the US Navy. Garrisons were effectively besieged and denied shipments of food and medical supplies, and as a result, some claim that 97% of Japanese deaths in this campaign were from non-combat causes.

Sources:
NSA.gov
The naval campaigns for New Guinea, Dr David Stevens