Why it was better to invade Luzon than Formosa

The short answer is that an invasion of Formosa in January 1945, not only would have been unnecessary but would have been a bloodbath. We would have incurred many casualties for no real benefit. The only real advantage of invading Formosa over Luzon was Formosa's geographic position. We could have cut Japan's sea lanes to the south more effectively from Formosa than Luzon. Otherwise the advantage would have been with Luzon. We would incurred more casualties for the following reasons:

1) We had occupied Luzon since 1900 and knew the detailed maps of the area along with Military officers who knew Luzon very well. Formosa had been occupied by Japan for almost 40 years, and we had no detailed maps or information on the island.

2) The Filipinos were on our side and provided us with valuable military intelligence. Such as the strength and location of the Japanese troops, existence of fortifications and blown and unblown bridges. The Filipinos not only used as scouts, but were valuable in containing and mopping up Japanese troops. The Formosa population would have contained large pro-Japanese elements that would have provided them with intelligence against us, and well as supporting guerrilla action against us.

3) Occupation of a mountainous, heavily forested island 240 miles long and 90 miles wide, with bad roads, would have required massive amounts of troops and negated our superiority in artillery and tanks.

4) Japan had millions of troops in China, and could have easily shipped reinforcements from China to Formosa. Formosa is only 100 miles from the China coast and 240 miles from Okinawa. On Luzon, OTOH, had only 250,000 japanese troops and no reinforcements arrived after our invasion.

5) The Japanese had 40 years to fortify Formosa against attack, and we didn't know their location and strength. By contrast the Japanese had only 3 years to fortify Luzon and we knew their exact location and strength.

6) With airfields in Leyte and Mindoro we were able to cover the landings in Luzon and suffer few losses. We invaded Luzon on Jan 9th 1945 and by Jan 15th the Japanese had launched their last Kamikaze attack and moved their remaining planes to Formosa. Furthermore, with adequate air cover form Mindoro and Leyte the Fast Carriers were able to cut loose in Mid January and continue their destruction of Japanese shipping and naval vessels in Indochina, Japan, and Okinawa.

7) By contrast, the only air coverage for the Formosa landings would have come from the CVE and the fast carriers. The Japanese would have been able to strike the landings not only from the Formosa airfields but stage them from Luzon and China. Indeed, even after we had occupied all of the Formosa, the Japanese still have continued their Kamikaze attacks from Chinese airfields.