Ships are whole new era for Contra, i have tons of ideas for them...for usa, china and gla....
you are not the only one,i have lots of ship ideas too,in general it could be like this:
rank1:light and medium ships\transports
rank3:heavy ships\special transports
rank5:aritllery ships that have long range and wtfbbqpwn everything,but are fragile.
of course it depends on the faction,for example stealth general,some special stealth transport(with some special ability of course) will fit more then a heavy ship,or for inf.gen the troop crawler will get a amphibious upgrade at rank 3,toxin gen will get something like dreadnought from ra2(but scud missiles of course),cyber will have more amph units then others,and etc...
now that i think of it,my ideas aren't that original(mostly rip off from ra2)
@Gen Kenobi:your naval stuff is awesome