The following is an attempt to pool all the available data which I have on the Thai Army of the "Indochina War 1940-41" between Thailand and French Indochina, hereafter described as the French-Thai War (FTW). More info on the AFVs can be found on Thai AFV Page, and the French are being researched by Nowfel Leulliot.
The Thais used the Adrian helmet, with a Thai royal crest on front. This gave a distinctly French appearance to their troops, but the uniforms are not exact copies of French styles. In fact, it more closely resembles the Japanese M90 uniform of 1930, which seems itself a development of the French WW1 uniform. (Thai troops in the Korean War still wore the Adrian helmet, but with a more "British BD" style of uniform). The French tank uniform does seem to have been worn, with overalls & specialist helmet. The uniform appears to be in a light khaki shade, and the Korean War helmets were brown in colour, which may also have been true in 1940-41. From photographs, the inter-war undress uniform has a distinctly Japanese/WW1 British appearance with unstiffened peaked caps.
1929 Uniform description :
Campaign dress is of khaki green material, jackets have upright collars. Troops are issued with a pair of shoes, wearing them is mandatory with parade dress and optional with campaign dress. Puttees are also issued to troops in same colour as uniform (plus one pair black for guard troops). Headdress is a Russian-style cap (the Siamese Army had strong links with Russia prior to this period).
Insignia : worn on shoulder boards and collar :
- officers wear a silver inverted grenade insignia on the collar
- rank & file wear the regiment's number on the shoulder boards and company number on the collar
- services : all officers and men wear a metal rose on their collar (this also applies to transport and ancillary services in the combat units, e.g. battalion qurtermaster)
- staff officers wear the Thai letters ST "Senatikam" (Staff) on their collar and a special insignia on their chest if they are graduates of the Bangkok Military Academy (Chulachomklao).
Some pictures taken from Chulachomklao Military Academy site:
The 1st regt/bn of every type (Infantry, Cavalry, Engineers, Artillery) seem to have been designated the "King's Own" or "King's Own Guard". In the case of the Infantry Guards at least, they were a largely ceremonial unit and fell out of favour in the 1932 upheavals. Hence, by the time of the FTW they were reduced to a "cadre" unit to guard the Royal Family, and are extremely unlikely to have been used in the fighting. The cavalry guards may, however, have been an armoured unit by then...
As the Siamese Army before it had been organised on French lines, and the new Thailand appears to have copied Japanese practices to a large degree, I would propose a structure for infantry similar to Japanese or French inter-war practices (and the Japanese formations were largely developments of French WW1 systems). In fact, French descriptions of Thai 1940 infantry organisation does sound very like the Japanese "Square" Infantry Division system. The AFVs are likely to have been organised either in independent formations like the French BCCs and Japanese Tank Regiment, or in Cavalry Regiments. Thus, in Command Decision terms, I propose the following:
Tanks mainly either Vickers 6-ton, Vickers Light or Vickers Carden-Loyd types (almost certainly in separate units).
There were 3 cavalry regiments, all apparently of battalion size, stationed in the Chantaburi/Pailin, Aryana Prathet/Poipet, and Ubon Ratchathani/Pakse areas. I do not know their designation, as 1st Cavalry Regiment seems to have been mechanized?
Thailand was divided into 18 provinces ("Montons") which were each responsible for raising troops. Therefore there may have been "provincial" regiments (in fact, Songgram raised about 50,000 troops for the FTW - which gives a figure of around 2,500 men per province, i.e. about a regiment). The 1917 conscription system (which appears to have still been in use in 1940-41) required every male Thai of age 21-22 years, and fit for service, to serve 2 years in the armed forces, with reserve service (in three age classes) after this (for 11 years?). King Rama VI had attempted to instill a "national service" ethic into the Thais, and Songgram also issued edicts aimed at encouraging nationalism. In addition to the army, a paramilitary gendarmerie was present in the 17 provinces outside Bangkok. These numbered approximately 7,000 well-disciplined men, but may well not have seen service in the FTW. Similarly, there were 2 battalions of Marines under naval control.
Much of the above from French military records, via Nowfel Leulliot (with thanks!)