French Indochina on the side of the Free French (1940)

Indeed, I am member of FFO...

In FFO, French-Thai war didn't occure before March 1941 and Japan wait until August 1940 to request closure of Chinese border which is refused by French, the reasons was France is still fighting and supported by United Kingdom.

I'm not sure Thailand would risk to invade FIC but, as proposed in FFO, local incidents prompted by Japanese military advisors would have degenerated in war.

It is unclear what would have happened if FIC joined FF. Here UK is still supporting FIC but, as explained by stevep ,, in the worst possible situation. Like stevep ,, I see Japan making the same pressure as IOTL but Thailand would probably stay more cautious because attacking FIC is being at war with UK and Commonwealth.

First, let see when and how FIC could join FF.

IOTL, general Georges Catroux rallied De Gaulle in July 1940 in Singapore, after leaving Indochina when replaced by admiral Jean Decoux sent by Vichy. One can imagine he decides to join FF with FIC (that is unlikely to happend because other political and economical leaders was conservative and closer to Petain). So let's assume FIC falls into FF beginning of July just before arrival of Decoux. Catroux already complied with the first Japanese ultimatum by closing the border on June 20. But general De Gaulle would likely order Catroux to resist to any other demand. It will likely degenerate in military escalation not from Japanese government but at the initiative of local commanders. But such an incident would provoque US oil embargo as retaliation. The marche to war will continue as IOTL.

In FFO, Japan takes advantage of Spratly Islands to create airfields in order to support Malaysia and DEI invasion. But FIC invasion still has to be done and will delay Singapore attack enought to allow Bitish to resist. This is probably the best case possible for Japanese in this scenario.

But an other option could be the border incident resulting in real war but probably later than september as Japanese will be more cautious about UK intervention, it's too early to launch war against Western countries.

In such a case, most of FIC will be invaded within two or three months (at least Tonkin and northern Annam) but China will help French to resist near the northern border. In the south, a British reinforcement in Saigon could have refrain Japanese to go South. One can imagine sort of ceasefire on the 17th parallel... Thailand would probably seize Laos and West Cambodia.

I see it would make it fair game if the Free French would declare Indochina as part of the De Gaulle government. Meaning Japan would attack it on December 8, 1941.

I was wondering, how would it look if French Indochina was on the side of the Free French in 1940 instead of going to Vichy France side.

Chinese had enought to do with their own front, they will only help Free French on the montaineous border area to avoid being taken in reverse. It could evolve if Catroux decide to reopen railroad to Yunnan, in this case, Chinese will have an interest to send troops but should they intervene before a Japannese invasion, it should have been a casus belli, and afterward, it won't be on time to avoid cutting railroad... At least, Catriux could discuss with Nationalists to prepare such an intervention but without good chance to succed in repelling Japannese.

You mean have Chinese troops station at the border waiting to move into French Indochina at the moment of a Japanese invasion.

One thing about this scenario, is that I think it is rather unlikely that French Indochina, alone of the major colonies, would be a major exception in going Gaullist/Fighting French and not Vichy. In OTL it was just Chad and then Cameroon Equatorial Africa at first, places that thought they might be on the chopping block for handover to Germany. Everyplace else was Vichy. Now in France fights on, where Algeria is the new capital, all the colonies stay pro-Allied, including Indochina.

Also, even if Vichy, I wonder if the French Indochina government might have tried to take a firmer, more resistant line if its capital wasn't so close to Japanese occupied China in Hanoi. Perhaps they would have felt less pressured and vulnerable if the colonial government had never moved there earlier in the century from Saigon, or had only moved as far north as Hue?