The category "<ship_class-creatable-sing>" can be expressed as follows:
aegis
aoe-6
assad
assad corvette
attack boat flotilla
cg-65
chosin
civilian freighter
civilian merchant
civilian tanker
corvette
csg-1
cvn-68
dd-963
ddg-72
fishing boat
freighter
harpers ferry
hudong
landing craft air cushioned
landing craft utility
lcac
lcu
lhd-1
los angeles
lpd-17
lsd-49
lupo
lupo frigate
mahan
mcm-1
mcs-12
merchant
mhc-51
missile attack boat
missile boat flotilla
nimitz
opfor sub
opfor submarine
pgm
rms
spruance
ssn-688
tanker
ticonderoga
trawler
wasp