By the summer of 1941, Japan's relations with the Western powers had deteriorated so much that Japanese leaders saw no point in delaying plans for military operations in Southeast Asia and the Pacific. Japan's short-term goal was to secure the necessary supplies to complete its conquest of China by occupying the Southeast Asian territories controlled by France, Britain, the United States, and the Netherlands. Japan's long-term plans called for further expansion south to Australia and north from Manchuria into the Soviet Union.
Japanese air and naval attacks on British and United States bases in Malaya and the Philippines were coordinated with the December 7, 1941, assault on the United States Pacific Fleet Headquarters at Pearl Harbor, Hawaii. Japan's Southern Army, headquartered in Saigon, quickly moved from bases in southern Indochina and Hainan to attack southern Thailand and northern Malaya on December 8 and the Philippines on December 10. The Japanese easily captured British air bases in northern Malaya and soon controlled the air and sea-lanes in the South China Sea as far south as the Strait of Malacca.
Naval landings were made on the Thai coast at Singora (present-day Songkhla) and Patani and on the Malayan coast at Kota Baharu. Also on December 10, the Japanese located and destroyed the Prince of Wales and the Repulse, thereby eliminating the only naval threat to their Malaya campaign. The Thai government capitulated to a Japanese ultimatum to allow passage of Japanese troops through Thailand in return for Japanese assurances of respect for Thailand's independence. This agreement enabled the Japanese to establish land lines to supply their forces in Burma and Malaya through Thailand.
The prediction that Japan would conquer the Malay Peninsula before attempting an invasion of Singapore proved to be correct. Lieutenant General Yamashita Tomoyuki was placed in command of the...