In early 1942, the Japanese, having occupied Rabaul and points on the northern New Guinea coast, decided to occupy the Solomon Islands and Port Moresby. This would enable them to deny the Allies bases from which to attack Rabaul and provide a springboard for attacks on Fiji, Samoa and New Caledonia. These operations would shore up the Japanese defensive perimeter while simultaneously cutting Australia's communications with the United States. Subsequently, Australia would either be forced out of the war or rendered harmless until a Japanese invasion could proceed at a more favourable time in the future. Australia's Combined Operations Intelligence Centre issued an assessment on 25 April that a Japanese assault on Port Moresby was imminent.
On 1 May 1942, two Australian cruisers sailed from Hervey Bay to rendezvous with an American force centred on the aircraft carriers USS Yorktown and Lexington. Three days later the Japanese Port Moresby Attack Force, carrying some 6,000 troops and supported by aircraft carriers, cruisers and destroyers, sailed from Rabaul. The Battle of the Coral Sea, which took place over the period 7-8 May, was in a tactical sense an inconclusive affair with both sides suffering the loss of a carrier. Nevertheless, the Japanese had failed to establish a sufficient level of sea control and, with their covering force depleted and air cover reduced, decided to postpone the Port Moresby operation.
In place of an amphibious operation the Japanese embarked on an overland advance from their bases on the north-east coast of New Guinea. In August, the struggle expanded to include Milne Bay, where the Allies were attempting to establish an air base. For the remainder of 1942, the pattern of fighting was characterised by a series of slow and costly engagements ashore. There were few incentives for the Allies to commit major naval forces. Ships of all types were scarce and, with the profusion of reefs and lack of accurate hydrographic information, operations close to land were inherently unsafe. Thus for the initial stages of the campaign and at least till the capture of Buna, direct naval assistance was limited to that provided by American motor torpedo boats and the small Australian corvettes.
However, although major offensive action by naval forces was no longer contemplated, maritime activity had not ceased. New Guinea had almost no land routes of communication, and so the war ashore was fundamentally dependent on seaborne logistics. In consequence, throughout the campaign both sides continued their operations in support of, or against sea communications.
Critical to the Allied campaign was the use of Australia as a rearward support base. Shipping movements along the east Australian coast and up to the forward areas increased rapidly as the land campaign got underway. After Coral Sea, the Japanese kept their surface ships north of New Guinea, so attempts to disrupt communications were generally limited to what could be achieved by their aircraft and submarines. The first serious attempt by the Japanese to disrupt shipping began in June 1942 with a sortie by five fleet submarines to the Australian east coast, and the midget submarine attack on Sydney. By August the Japanese had sunk seven merchant ships and damaged another six. These losses were comparatively small on a worldwide scale, but were magnified by the growing supply needs of Allied forces in New Guinea and the severe shortage of ships everywhere.
Allied escort and convoy arrangements began in an ad hoc manner but, as the land campaign progressed, such arrangements could not be sustained. Australian coastal convoys began in June 1942, while regular routine convoys from Townsville to New Guinea began in December and continued to operate until March 1944. Over this period more than 1,100 merchant ships safely made the journey to New Guinea in 254 convoys. In addition there were many special and troop convoys. By early 1943 there existed a complete system of convoys that stretched from Melbourne to advanced New Guinea bases. It was a sophisticated system, and one that proved remarkably efficient, but its success was aided by the Japanese inability to maintain a consistent anti-shipping campaign.
The establishment of the US Seventh Amphibious Force in January 1943 heralded a return to the offensive by Allied naval forces in New Guinea. Supported by ever-increasing strength at sea and in the air, Allied troops were for the first time able to take full advantage of amphibious mobility and heavy naval firepower. Strongly garrisoned Japanese positions were bypassed and troops landed on lightly or undefended beaches. In contrast to the earlier overland offensives, amphibious operations reduced losses and increased the speed of advance.
The Japanese, on the other hand, were hampered by an ever-tightening stranglehold on their supply lines. Although they managed to maintain an offensive posture for most of 1942, by the end of the year Allied air and submarine attacks on their poorly defended convoys were becoming increasingly effective. Heavy equipment, food and ammunition were in short supply, while difficulty in maintaining an adequate supply of spare parts severely reduced Japanese air strength. In January 1943, the US submarine Wahoo reported that it had sunk all four ships in one enemy convoy. Two months later a successful Allied air attack in the Bismarck Sea destroyed what was to be the last major resupply operation attempted by the Japanese. Thereafter, the Japanese abandoned hope of any further offensive operations on land and isolated areas became almost totally reliant on submarines and small barges for resupply.
Although safer than other methods, supply by submarine could not substitute for an efficient transport service. Between December 1942 and September 1943 Japanese submarines made 95 trips to New Guinea, delivering 3,500 tons of cargo. In June 1943 alone, the Allies moved more than 55,300 tons from Milne Bay and Port Moresby to forward areas. By September, the monthly total had increased to over 200,000 tons of cargo. Subjected to such an extremely effective blockade, Japanese troops suffered terribly from illness and malnutrition.
The activities of naval forces directly contributed to the ultimate fate of New Guinea. For both sides the protection of their sea lines of communication while interdicting the enemy's was a vital adjunct to the successful progression of the land campaign. The Japanese failure to allocate sufficient priority to either a concentrated offensive against enemy shipping, or protection of their own convoys ensured that Allied material superiority must eventually triumph. In turn, once they had achieved superiority Allied naval forces allowed MacArthur to achieve his objectives with remarkable speed and economy.
Naval campaigns:
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