Two things of which you should be aware:
1. The list of maximum numbers of SBDE efficient units by type:
i. Aircraft – Interceptor – 5
ii. Aircraft – Naval Bomber - 5
iii. Aircraft – Strategic bomber – 5
iv. Aircraft – Tactical bomber - 5
v. Anti air – 8
vi. Anti air – SP – 6
vii. Anti tank – 8
viii. Artillery - 8
ix. Artillery – SP – 6
x. Armored car – 8
xi. Infantry – Commandos - 8
xii. Infantry – Infantry – 8
xiii. Infantry – Mechanized - 6
xiv. Infantry - militia - 11
xv. Infantry – motorized - 8
xvi. Naval - Battleships – 3
xvii. Naval – Carriers – 3
xviii. Naval – Cruiser – 5
xix. Naval – destroyer - 7
xx. Naval – submarines – 8
xxi. Tank - destroyer – 5
xxii. Tank – heavy – 5
xxiii. Tank – light - 6
xxiv. Tank – medium - 5
xxv. Aircraft - Rocket fighter - 5
xxvi. Railroadgun - 3
The original list was compiled by former administrator @BRDubbs. All credit goes to BRD; I'm merely re-posting his handiwork here.
Here is COW combat calculator programmed by forum member @DxC:
It is brilliant. If you have any particular questions about the calculator, put them directly to DxC -- there's no-one better to answer questions about its mechanics.
Cheers.