Spoiler


More possible planes:
Vickers E.F.B.7 armed with 37 mm cannon,

Breadmore W.B.V armed with different 37 mm, Le-Puteaux cannon.

While never reaching operational status and being unreliable some aircrafts did carry “special” 1.59-inch breech-loading Vickers Q.F. gun, Mk II.
Vickers F.B. 25

and Royal Aircraft Factory N.E.1

I am in favor of WW1-interwar vehicles.
I do have issues with current tech tree. The replacing reserve tier or ranks 0-0.7 would not be ideal in this case.
But I think tech tree issues are a separate thing, so your mini tree “rank 0” looks good at a first glance.
Would also flesh out the Hungarian tree within Italy (Austro-Hungarian obvs.)
I am in process of making TT of A-H + what Swiss had :). I would not make it part of Italy though since they were enemies during the war.
World War 1 vehicles are a must
+1
Bring Back WW1, return to roots!
+1