Rather than an ammo ship, I would suggest a new line of support ship, with increase number of sailor slots, ammo space, and plane space, much like the CV line.
The support ships will generally have 2 gun slots, and varying support slots. The guns they carry should be for self-defense only, perhaps use the sub guns? The sailors that they can consider carrying are:
- Gunners: to use guns, and needed to replenish ammo for other ships
- Repairer: repair other ships
- Engineer: act as a tow boat, towing back crippled ships. No effects on undamaged ships
- Restorer: increase his own SD, so the ammo ship doesn't go boom when one-hitted
- Scout: Fly scout plane, and replenish scout planes
- Ftr, DB, TB: needed to replenish Ftrs, DBs, and TBs respectively. Cannot use these types of planes
- Medic: revive crew (sailor, skilled sailor, officers) killed for other ships. If no crew is killed, no effect
- Seaman: General increase in ability for other ships
In terms of the ammo, I would suggest that ammunition ships have to carry different types of ammo, as follows:
- HE shells
- AP shells
- AA shells
Just like CVs can't pack 1000 scouts, ftrs, DBs and TBs at the same time, ammo ship will have to pick and choose how much and what they want to carry. So if they carry only HE shells, then they can replenish all ships requiring HE shells, from 3" to 20", but they won't be able to help subs and TW with torps, or AA ships with shells, etc. Or they can mix and match different types of ammo.
Support ships should be able to launch scouts, and replenish other ships of scouts, Fts, DBs, and TBs. Again, there's a fixed aircraft space, and they have to mix and match.
Sorry for this long post, but I have given this quite some thought, and I think it can be a useful ships in many different ways. And given that you have to choose what sailors to load, and how much ammo and planes, it can be quite customizable.
BTW, where did the sprite come from? it looks very NF like. If it's photoshopped, then good job.