The '2^nd Operational Phase' was the plan created by Japan’s military leaders for the exploitation of their successes in the 'Centrifugal Offensive', which ended with the surrender of Java on 8 March 1942 (7 March/August 1942).

The Japanese had achieved all their initial war objectives ahead of schedule and with astonishingly slight losses in the 'Centrifugal Offensive'. Instead of the 20% to 30% naval losses anticipated in their pre-war planning, the Japanese had lost only 23 warships, all of destroyer or smaller size (for a total of 26,441 tons), 67 transport and cargo ships (for a total of 314,805 tons) and a few hundred aircraft and a few thousand personnel. This astonishing success was misread by the vast majority of Japanese planners, who signally failed to recognise that the Allies would learn from bitter experience and that US mobilisation, of both manpower sand industry, was certain to effect the rapid elimination of Japan’s current military superiority. Rather than consolidate their conquests and build their defensive perimeter, then seek a diplomatic settlement on favourable terms as originally planned, the Japanese began looking for new worlds to conquer. After the war, Vice Admiral Chuichi Hara, latterly the command of the 4^th Fleet, characterised this unrealistic attitude as the 'victory disease', and there is wide consensus that the carelessness brought on by this attitude led to the Japanese setback in the 'Battle of the Coral Sea' and the disaster in the 'Battle of Midway'.

'Victory disease' was not universal, however, for Emperor Hirohito, for example, asked General Harime Sugiyama, chief-of-staff of the Imperial Japanese army, whether the fall of Singapore in February 1942 might not be an opportune time to seek a settlement with the British. Most of the army leadership was anxious to finish the wars in the Pacific and in China in order to redeploy against the USSR, which had unexpectedly survived the German 'Barbarossa' invasion of 1941. However, the debate within the armed services over the future course of the war ended on 7 March 1942 with a liaison conference at Imperial General Headquarters that mapped out the '2^nd Operational Phase'.

The '2^nd Operational Phase' was largely the strategy of the Imperial Japanese navy as the Imperial Japanese army was so preoccupied elsewhere. A direct invasion of Australia was urged by the navy, which estimated that three army divisions would be sufficient to seize the continent’s important centrs, but on 7 March 1942 the army vetoed this plan, claiming that the actual requirement would be 12 divisions and 1.5 million tons of shipping. The compromise objective was to isolate Australia, forcing it out of the war, and to seize the Hawaiian islands group as a forward base. Alaska would then be ripe for the picking, and some Japanese leaders even looked ahead to the seizure of portions of Australia and the US states of Washington and Oregon. The Pacific would thus be transformed into a Japanese lake.

It has been argued that the best option for Japan would have been to remain on the offensive for the '2^nd Operational Phase', for the retention of the initiative would have been best hope for Japan to offset US matériel superiority, and that the optimum strategy for Japan would have been to focus on the severance of the sea lanes between the USA and Australia. Instead, the Japanese planned a series of advances along two axes that in many respects resembled those of the Allied counter-offensive of 1943/44, but in reverse. The first blow would fall on Port Moresby and Tulagi early in May 1942 ('Mo'), projecting Japanese power over the Coral Sea and opening the way to the New Hebrides and New Caledonia island groups. This would be followed by the capture of Midway ('Mi') and the western Aleutians ('Al') in June. In July it would be the turn of the Fijian and Samoan island groups ('Fs'). Finally, Hawaii would be assaulted in October. Admiral Isoroku Yamamoto, commander of he Combined Fleet, believed that 'As a result of the smooth progress of the first-phase operations, we have established an invincible strategic position [that] cannot be maintained if we go on the defensive…in order to secure it tenaciously, we must keep on striking offensively at the enemy’s weak points one after another.'

The Japanese did not detect the Allied build-up on the islands along the sea lanes between the USA and Australia, and the forces they allocated for the southern prong of the '2^nd Operational Phase' were 'completely inadequate' to deal with the reinforced island garrisons

The Allied defensive strategy was shaped largely by Admiral Ernest J. King, the US chief of naval operations, who was not content with standing on the defensive and waiting for the Japanese exploit their initiative. King insisted that Admiral Chester W. Nimitz, commander of the Pacific Fleet and Pacific Ocean Areas, conduct carrierborne raids against outlying Japanese positions to keep them off balance, while protecting the Hawaiian islands group and the sea lanes to Australia. King also looked to an early counter-offensive from the New Hebrides islands group up the chain of the Solomon islands group to the Japanese pmary base at Rabaul on New Britain island. This eventually materialised as the 'Watchtower campaign on Guadalcanal and its successors.

In retrospect, Japanese plans for the '2^nd Operational Phase' were completely unrealistic, and thus it should be no surprise that the Allies managed to stop the Japanese. The 'Battle of the Coral Sea' frustrated the attempt to seize Port Moresby, but Yamamoto chose to regard this as a minor and temporary setback and proceeded with the Midway operation. The 'Battle of Midway' was a strategic disaster for Japan as the Imperial Japanese navy lost most of its first-line carriers, a blow from which it never really recovered. The battle restored the balance of power in the Pacific, and the Americans seized the strategic initiative with the counter-offensive on Guadalcanal.

Quite extraordinarily, the Japanese continued in their gross underestimation of the US forces even after the Midway disaster. Japanese senior commanders, including Yamamoto and Vice Admiral Shigeyoshi Inoue, remained convinced that the Allied could not launch any significant counter-offensive before the autumn of 1943. The Japanese briefly continued developing plans for the Fiji-Samoa operation following Midway, but on 11 June 1942 'Fs' was postponed for two months. However, the 'Ri' land operation against Port Moresby over the Kokoda Track, was to proceed. On 17 June the Japanese approved the 'Sn' operation, ordering the airfield at Guadalcanal ready by the middle of August to receive 27 fighters and 27 medium bombers. The main 'Sn' convoy departed Truk in the Caroline islands group on 29 June and arrived at Guadalcanal on 6 July with 2,600 construction troops and 250 combat troops.

However, Japanese plans continued to evolve as the consequences of the 'Battle of the Coral Sea' and the 'Battle of Midway' became clearer. On 11 July 1942 'Fs' was canceled entirely, and in its place the Japanese began looking to the Indian Ocean, where light forces based in Burma could conduct a raiding campaign against British commerce. This operation was called off after the US landings on Guadalcanal, and the cruisers were redeployed to participate in the campaign to retake Guadalcanal.
Any remaining thoughts of advancing against Fiji and Samoa were quietly dropped when the Americans could not be dislodged from Guadalcanal.