This was an US unrealised plan for the seizure of the Japanese-held islands of Formosa and Amoy (August 1944).
Created by Admiral Chester W. Nimitz’s Pacific Ocean Areas command, and initially scheduled for implementation during February 1945, this undertaking was the subject of considerable debate as a result of the strength of the expected defences, the lack of adequate US assault forces, and the considerable distance that land-based aircraft would have to cover in order to provide air support. The operation was ultimately put into abeyance (but never formally cancelled) in October 1944 as better opportunities were offered by ‘Detachment’ against Iwo Jima and ‘Iceberg’ against Okinawa, followed later by the ‘Olympic’ and ‘Coronet’ direct assaults on the Japanese home islands.
The object of ‘Causeway’ (ii) was to provide the Allied (especially US) forces with a springboard for air, naval and amphibious operations against the major Japanese forces fighting in China. Had it proceeded, ‘Causeway’ (ii) would have involved 302,000 men of the US Army and 100,000 men of the US Marine Corps, and would have started with the landings of single divisions of Major General Roy S. Geiger’s III Amphibious Corps and Major General John R. Hodge’s XXIV Corps, of Lieutenant General Walter C. Krueger’s 6th Army, on the south-west coast of the island between Kaoshiung and Kenting. The steadily reinforced US forces would then have consolidated their control of the southern one-third of the island before advancing northward along the west coast, which had far better communications than the east coast, toward the Japanese colonial administrative centre at Taipei near the northern tip of the island.
The final nail in the coffin of ‘Causeway’ (ii) was the implacable opposition of General Douglas MacArthur, who believed that the any decision for the implementation of ‘Causeway’ (ii) would have denied his South-West Pacific Area command the chance for the US return to Luzon island in the the Philippine islands group, whose liberation MacArthur had promised when he left the islands in 1942.