The Imperial Japanese Army (IJA) and the Imperial Japanese Navy (IJN) used several designation systems which differed only marginal for land-based weapons (compared to the airforce and naval designation systems). Most designations had the same basic appearance:
Yeartype - sort of equipment - (not always) short designation - (not always) additions
The Yeartype consisted mainly of a number indicating the year of introduction or design begin and the syllable "shiki" for "Type" or "Model" (which is still not finally clarified among experts, most tend to "Type").
Until 1940 the year was used in which the weapon system was officially introduced (e.g. Type 95 Light Tank) or finally refused (e.g. Type 95 heavy tank). From 1941 on this system was not longer used that strictly, mainly to hamper enemy intellicgence (e.g. the Type 3 medium tank was introduced in 1944, design was started in 1943).
If there are different weapon systems of the same type introduced in the same year the supplement "model" and a number was added. (e.g Type 94 Model 1 - 4 for four different sized radio sets). Changes in the design of a particular "model" was indicated by the further addition "Mark" and number (eg. Type 94 Model 2 Mark 3 bomb fuze).
For the year of introduction two different calendar systems were used:
With this system the additional syllable "nen" = "(regency) year" was added between year and "shiki". The year is given as "Year of regency" of a particular emperor:
To simplify the designation system and to reduce irritations if the Regency addition wasn´t added completely (e.g. if only "juichi nenshiki" = "Type (regency) year 11" is mentioned it could mean a 1923 = Taisho 11 or 1936 = Showa 11 introduced weapon system) IJA and IJN changed from regency year to Jimmu-calendar year in 1928.
But many navy and airforce design orders were designated after the Showa-calendar (e.g. The design of the A6M "Zero" started as "Navy experimental 12-Shi Carrier Fighter" in year 12 of Showa regency = 1937.)
The Jimmu-Calendar is based on the more or less mythical beginn of the japanese empire. In 660 BC (in 1872 the 11. February was declared as "correct date") a local leader defeated the last larger local enemy and founded the japanese imperial dynasty. He later received the honor name Jimmu. For more informations click here. So the standard japanese calender which is still in use began in 660 BC.
From 1928 on IJA and IJN designated their weapon systems using the Jimmu-Calendar-year. 1928 was year 2588. To simplify this system only the last 1 or 2 ciphers were used (2588 = 88, 2604 = 4). For 1940 the possible year designations 0 and 100 were both taken (IJA used 100, IJN 0).
In general the same designations as in western armys were used, translated into japanese language (e.g. light tank, rifle, handgrenade, radio set, gas mask etc.). Sometimes designations were somewhat different but more or less self-explanatory (e.g. "Ju-Sokosha" = "heavily armoured vehicle" for the small Type 92 recon tank used by cavalry units; "recoilless rifle/gun" for rocket-propelled at-weapons and artillery rocket launchers, IJA did not have real recoilless rifles/guns; "kikanho" = "automatic cannon" for light aa-guns).
Several japanese vehicles received short designations. Some of these designations were part of a system (e.g. light and medium tanks, gun tanks etc.), others had to do with the intended tasks (e.g. special tractor, gun carrier, armoured vehicle etc.) or were added during development and officially adopted later (e.g. "Ha-Go" or "Ka-Mi") Some meanings were lost during the years but most are still known. I will cover this topic in a later post here.
Several pieces of equipment received additions to clear the identity of the piece of equipment. Often used were the following: