Well, it was, Montengro that is. For one thing at least it was indeed in Montenegro

(and an Italian vasall, but hey, nobodys perfect!)
The NDH I might agree with, but "Montenegro" was a name and perhaps four battalions. The Germans raised as many Norwegians. The Prince of Montenegro, to his credit, had nothing to do with it. It was ruled by Italian govenors, it never even nominally administered all its claimed territory, and most of the
collaborators in it were Chetnik. Even among the uniformed traitors, half of them were called "Serbian"!
Perhaps I should have said the Independant State of Macedonia.
Anyway, the point is that it's an insult to Indians, who organised the largest volunteer army in the history of the world against fascism and then went on to win their independence by peaceful methods in an unprecedented way, to say that Bose and his gang, who were used as
coolies by the same Japanese authorities that slaughtered Indians on the Andaman islands, were an "Indian insurgency".
And to be less emotive, it's not relevant to the (long-dead) topic. They were part of the conventional war in Burma. Britain gained no "experience in fighting insurgencies" from them.