This is the wholly unofficial but much used designation accorded by US historians to the first Japanese offensive of the Pacific War, which was centred in South-East Asia but also included the 'Ai' attack on Pearl Harbor and subsidiary operations intended to secure the flanks of the main advance (September 1941/April 1942).
The roughly synonymous Japanese term for this offensive is 'Strike South', and its objective was the capture of the resource-rich Western colonial possessions in South-East Asia and the establishment of an impenetrable defensive perimeter to ward off any Allied counter-offensive. Once these objectives had been attained, the Japanese government intended to seek a negotiated settlement on terms favourable to Japan.
The Imperial Japanese army and navy each favoured a different strategy for the opening offensive of the Pacific War. The army preferred an attack on Malaya, followed by the Netherlands East Indies, then the Philippine islands group in the belief that Malaya would difficult to take and should therefore be seized before the British could send significant reinforcements. The navy preferred almost the opposite strategy, fearing that US air power in the Philippine islands group would endanger the Japanese maritime lines of communication to the Netherlands East Indies and Malaya if the Philippine islands group was not neutralised first.
The compromise reached was to secure both flanks at once. The Japanese were encouraged by the German success in using land-based aircraft, over Norway and elsewhere, in the face of superior Allied naval power, and therefore planned simultaneous offensives on two fronts. The first front was directed primarily against Malaya and also Sumatra and western Java in the Netherlands East Indies, but was also to seize key locations along the west coast of Borneo. The second front began with the Philippine islands group and proceeded through the Makassar Strait to eastern Java in the Netherlands East Indies.
The western flank was to be covered by the occupation of Thailand and Vichy French Indo-China, and the eastern flank was to be protected by seizing strategic points in the eastern part of the Netherlands East Indies, particularly in the Lesser Sunda islands group and western New Guinea.
The remainder of the Japanese defensive perimeter in the Pacific was extended by seizing Kavieng on New Ireland, Rabaul on New Britain, the Gilbert islands group, Wake, and Guam in the Mariana islands group.
Each advance was to proceeded by leaps, each of the leaps being directed against a strategic point having an airfield which could be developed rapidly to Japanese use to provide air cover over the next leap, and thus each leap was short enough to be easily covered by land-based aircraft. Air units would then move forward to the newly captured airfield to cover the next leap. The Japanese carefully planned the offensive on a strict timetable to keep the Allies off-balance and unable to redeploy in time to meet each new threat. This strategy was successful largely because of Japanese supremacy in the air and superiority at sea.
From September 1941 the Japanese navy conducted extensive map exercises, and these continued through October. The plan was a significant departure from the 'Decisive Battle Doctrine', most particularly in the determination of Admiral Isoroku Yamamoto to abandon a fundamentally defensive strategy and take direct offensive action against the US Pacific Fleet at the very start of hostilities. Although the notion of a surprise attack on Pearl Harbor in the Hawaiian islands group was not new, it having been war-gamed by the US Naval Staff College as early as 1927, only Yamamoto had the prestige to reverse years of settled doctrine and force the navy general staff to accept the plan.
Most of the Japanese landings were unopposed, which was possible because the Allies lacked adequate numbers of troops to cover all the possible landing beaches available to the Japanese as a result of their naval superiority.
The Allied defensive strategy was hampered by air and naval inferiority and by the difficulties of coordinating between four different nations involved, namely the UK, USA, Netherlands and Australia. The American-British-Dutch-Australian Command created to co-ordinate the Allied defence was plagued by conflicting national priorities and goals, was established too late to operate smoothly.
The very weight and speed of the Japanese offensive meant that the ABDA Command was never able to gain the initiative, and even its reactions to perceived Japanese thrusts were sluggish. With the fall of Manila and Singapore, there was not a single port in South-East Asia in which the Allies could base warships larger than heavy cruisers, and there was no logistical infrastructure to allow the movement of major reinforcements into the theatre, even if such reinforcements had been available.
By contrast, the Japanese had available excellent facilities in Vichy French Indo-China, the Palau islands group and Formosa island, all close to the various parts of the strategic target area.