American and Japanese military records have a discrepancy on the Japanese order of battle on Attu at the time of the American landings. Although similar they vary sometimes by several hundreds of men. Some after action reports from the US Army are very accurate, however they do not give a break down of unit names, strength, and branches of the Imperial Japanese Forces. In the most recent accounts of the battle by western sources there is the stereotyped grouping of all Japanese units into one amorphous mass, as if the numerous combat arms were the same. This masks the complexity and difference of the Japanese Imperial forces. While western military forces have similar organisations the difference in the Japanese combat arms reveals a marked nuance how Japan deployed and supplied troops.
During the battle of Attu the overwhelming majority of Japanese defenders were from the Japanese Army. But there were also Naval elements under command of naval officers – particularly the Japanese weather observatory unit that was staffed by highly trained meterologists and the naval radar detachment.
Also, importantly was the presence oft two large Japanese anti-aircraft batteries which were very successful in pinning down the Americans after they landed in Holtz Bay. Their presence tell of the importance the Japanese High Command placed on defence of the island from American air attacks while the airstrip was being built. These guns were used on a flat trajectory to fire across Holtz Bay upon the American forces and to cover the Japanese defending the “Grassy Knoll” (Shiba-Dai 芝台) posiiton (know as “Hill X” in American combat records.”
All members, even civilian attached personnel were expected to fill out the roles of fighting personnel.
Japanese Order of Battle from Start of American Landings on Attu.
1) The table below is from a compendium in the Book “Gyokusaisen: Attu Tou「玉砕戦アッツ島 」Annihilation Battle of Attu, by Ushijima Hidehiko, 1999 edition, Kojinsha Publishing. Chiyoda Ku, Tokyo.
From page 85
Japanese Attu Order of Battle:アッツ島守備隊戦闘序列 米軍上陸之際
Chichijima Fortress Defence Corps – 30 officers, 91 noncommissioned officers, 326 other ranks) (includes civilian attached functionaries 軍属) total 747
303 Independent Infantry Battalion – 32 officers, 17 non-commissioned officers, 560 other ranks, total 609
Northern Defence Command Personnel Section 北守司令部人員の一部 – 6 officers, 11 non-commissioned officers and 35 other ranks, total 52
Field Anti-Aircraft Units
24 Anti-Aircraft Battery – 6 officers, 10 non-commissioned officers, 192 other ranks – total 218
33rd Anti-Aircraft Battery – 7 officers, 23 non-commissioned officers, 180 other ranks – total 210
302 Independent Engineering Company – 5 officers, 20 non-commissioned officers, 149 other ranks – total 174
2co/6th Marine Transport Engineering Regiment – 船舶工兵 (see note below)- 6 officers, 27 non-commissioned officers, 168 other ranks – total 201
11th Independent Signals Section – 1 officer, 7 non-commissioned officers, 14 other ranks – total 22
30th Anchorage Section – 弟三十停泊熱田支部 – 2 officers, 3 non-commissioned officers, 43 other ranks including 6 attached civilians 軍属 – total 47
Ohura Field Hospital Section; Named after their commanding officer Ohura Shiro (or possibly Niroo) 大浦二郎 – 7 officers, 6non-commissioned officers, 34 other ranks – total 47
Atta Detachment Naval Section (Imperial Japanese Navy) – 1 officer, 7 non-commissioned officers, 14 other ranks – 22 total
Naval Radar Detachment 電波探信機 ( Imperial Japanese Navy) – 1 non commissioned officer, 36 other ranks (including attached civilians) 軍属 – total 37
Japanese Army Postal Corps – 1 officer, 5 non-commissioned officers, 8 other ranks (included attached civilians 軍属) – total 14
Total Japanese service personnel on the island at the time of the American Landing was:
302 non-commissioned officers
2206 other ranks including attached civilians
These troops called Senpaku Kohei. For a futher explanation kindly read footnote number 19 on the battle of Attu.