This is the 13208th most frequent Polish word.
okrętów
The Polish word "okrętów" means "of ships" (genitive plural of "okręt").
Here, 'okrętów' is the genitive plural form of 'okręt', used after a quantity phrase.
Flota składa się z pięciu dużych okrętów.
The fleet consists of five large ships.
'Okrętów' is the genitive plural case, used here after the verb 'nie widziano' (was not seen).
Nie widziano takich okrętów na naszych wodach od wielu lat.
Ships like these haven't been seen in our waters for many years.
In this context, 'okrętów' is used in the genitive plural form to indicate possession or relation.