Until the Royal Air Force captured a Nakajima Ki-43 Hayabusa virtually intact in the spring of 1942, Allied pilots knew little about the planes they were meeting in the air, and even less about the Japanese Army Air Force units opposing them. The situation has improved very little over the years. JAAF records of the air war in the Pacific are necessarily sketchy, since some units -- including the 77th fighter sentai that bore the brunt of combat against the AVG -- were destroyed during the terrible retreats of 1944 and 1945. (Curiously, the records of the 77th were among the few that survived the war.)
Less understandably, few westerners have troubled to to use the Japanese sources that are available, and that are now becoming available in increasing numbers. Often, therefore, I been obliged to make my own translations, with the help of young people with little knowledge of military matters; this work was necessarily crude, and represents only a small beginning on what should be done. For example, there are at least six books about the 64th Sentai, beyond those I worked with. (Since this was written, John Lundstrom in the United States and Christopher Shores in Britain have done great work in writing about Japanese navy and army air operations.)
The basic Japanese air combat unit was the sentai, equivalent to a USAAF group, though with only half the aircraft. With an effective strength of between 30 and 40 aircraft, the sentai was commanded by a major or lieutenant colonel who was himself a flying officer. The sentai in turn was divided into three chutai, or squadrons, usually commanded by a captain. Occasionally a chutai might be detached for service in an isolated area, or an "independent chutai" would operate on a continuing basis outside the usual command structure. (An independent chutai was a bit like a Royal Air Force squadron, which could move from place to place with its own headquarters staff, attaching itself to whatever group or wing was already there.)
Moving up the chain of command, two or more sentais -- often a fighter group, a heavy-bomber group, and a light-bomber or ground-support group -- made up a hikodan, equivalent to a USAAF wing and usually commanded by a colonel. Two or more hikodans made up a hikoshidan, equivalent to a geographical air force and commanded by a general officer.
At the outbreak of the Pacific War, the JAAF consisted of five hikoshidans with a total of about 1,500 aircraft. One of these was assigned to home defense, another to Manchuria, and a third to China, leaving two to go on the offensive in the South Pacific. The 5th Hikoshidan took part in the invasion of the Philippines, its heavy bombers flying from Taiwan to hit targets in northern Luzon, while its fighters and light bombers operated from airfields seized in the opening days of the war. When U.S. and Filipino forces were driven back upon the Bataan Peninsula, most of the 5th Hikoshidan returned to Taiwan for reassignment.
Meanwhile, the 3rd Hikoshidan operated against British Commonwealth forces in Malaya, along with three sentais detached from the 5th. They were based in French Indochina until fighting began, afterward moving to bases seized in Thailand and Malaya. That no warplanes appeared over Rangoon until December 23 was a tribute to the resistance put up by Commonwealth air forces in Malaya: only after the situation was well in hand there did General Michio Sugawara make his first move against Burma.
By mid-January, with Malaya likewise under control, the 3rd Hikoshidan had shifted its attention to the Dutch Indies. Meanwhile, the 5th Hikoshidan under General Eiryo Obata moved into Thailand, rejoined its three detached sentais, and mounted the major air campaign against Burma.
Japanese ranksOn the left is the Japanese army rank, followed by its equivalent in the U.S. Army and Marine Corps and then by its U.S. Navy equivalent. The JAAF made no distinction between air crew and ground personnel, at least for period 1941-1944. The Japanese navy used these same ranks for all officers except tai-i, which it rendered dai-i; enlisted personnel had job- specific titles that changed on two occasions, making them too complex to be listed here.
Heicho -- Private / Seaman
Gocho -- Corporal / Petty Officer
Gunso -- Sergeant / Petty Officer
Socho -- Master Sergeant / Chief Petty Officer
Jun-i -- Warrant Officer
Sho-i -- Second Lieutenant / Ensign
Chu-i -- First Lieutenant / Lieutenant j.g.
Tai-i / Dai-i -- Captain / Lieutenant
Sho-sa -- Major / Lieutenant Commander
Chu-sa -- Lieutenant Colonel / Commander
Tai-sa -- Colonel / Captain
Sho-sho -- Major General / Rear Admiral
Chu-jo -- Lieutenant General / Vice Admiral
Tai-sho -- General / Admiral