The category "<ship_class-not_creatable>" can be expressed as follows:
aegis
aegises
aoe-6
aoe-6s
assad
assad corvette
assad corvettes
assads
attack boat flotilla
attack boat flotillas
cg-65
cg-65s
chosin
chosins
civilian freighter
civilian freighters
civilian merchant
civilian merchants
civilian tanker
civilian tankers
corvette
corvettes
csg-1
csg-1s
cvn-68
cvn-68s
dd-963
dd-963s
ddg-72
ddg-72s
fishing boat
fishing boats
freighter
freighters
harpers ferries
harpers ferry
hudong
hudongs
landing craft air cushioned
landing craft utilities
landing craft utility
landing crafts air cushioned
lcac
lcacs
lcu
lcus
lhd-1
lhd-1s
los angeles
los angeles's
lpd-17
lpd-17s
lsd-49
lsd-49s
lupo
lupo frigate
lupo frigates
lupoes
mahan
mahans
mcm-1
mcm-1s
mcs-12
mcs-12s
merchant
merchants
mhc-51
mhc-51s
missile attack boat
missile attack boats
missile boat flotilla
missile boat flotillas
nimitz
nimitzes
opfor sub
opfor submarine
opfor submarines
opfor subs
pgm
pgms
rms
rms's
spruance
spruances
ssn-688
ssn-688s
tanker
tankers
ticonderoga
ticonderogas
trawler
trawlers
wasp
wasps