IL2 Sturmovik most certainly does this, spent many hours playing coop missions with squad mates.
Cool!
Couple of questions please...
- What IL2 are we talking about?
- Are the missions fairly interesting?
- Can you get upto 6 of you playing (PvE)?
- I assume you need to download, setup and run your own server?
Nothing springs to mind I'm afraid, but War Thunder does allow squads of up to 4 people to join the same battle, although it doesn't have a decent PvE system.
Not sure if any of the other mission types in the game allow for PvE in squads, I've never looked into it.
So:-IL2 Sturmovik 1946, unsure how Cliffs of Dover works for Coop as I've never played it that way.
Missions vary obviously, there are hundreds available though.
6 and more
If I recall correctly you host from the game and give people IP address to connect to, or use Hyperlobby (http://hyperfighter.sk/) to find/host Coop games and connect from there.
Thanks...Il2 1946 and il2 cliffs of Dover can be hosted from the game and your friends connect through ip. As does rise of flight (ww1).
Rise of flight is free for the Base game and some free planes, and is wonderful.