The category "<ship_type-not_creatable-sing>" can be expressed as follows:

<ship_type-not_creatable-sing>

<ship_class-not_creatable-sing>

<ship_class-not_creatable-sing> <type_of_ship-sing>

<ship_class-not_creatable-sing> class <type_of_ship-sing>

<type_of_ship-sing>