These are upgrades that improve a plane's combat abilities in some way, and use Combat upgrade slots on a plane. For a list of all upgrades, see Category:Upgrades.
“This upgrade also increases the combat level by + 5 and increases the number of mission offered...Sleigh Bell
“Never run out of ammo in those tight situations when surrounded by villainous pirates out for...Super Ammo
“ Mega Ammo Upgrade Category: Combat Upgrades Oh my gosh, I just can't believe how long you can...Mega Ammo