As they are beefed up mountain troops you can use them in mountains regions. Like in some parts of Middle East and Asia UK provinces or enemy provinces. They also have some bonuses in jungle, woods and forests. They don't have huge bonuses, but are good in many terrains. Also, they can paradrop.
Gurkha vs mountain infantry:
+10 organisation/+5% morale
-3 transport weight/+0.5 armor penetration
+10% better attack in mountains/+5% faster movement in mountains
+10% better attack in hills/+5% faster movement in hills
+10% better attack in jungle/+5% better attack in forests/+5% better attack in woods
So, i just use them like i would use mtn infantry? Alright. Going to make 3 or 4 divisions of those for the indian theatre.
By the way, as the UK, germany has nearly wiped out France, except for the northeastern zone, that the BEF is holding. Why hasnt Italy joined the war yet? its February 1940.