This is the 2115th most frequent Polish word.
oficerów
"Officers" (genitive plural form in Polish).
Here, 'oficerach' is the locative plural form of 'oficer,' meaning 'officers' in the context of what the command relied upon.
W czasie wojny dowództwo polegało na oficerach.
During the war, command relied on officers.
In this sentence, 'oficerów' is the accusative plural form of 'oficer,' referring to the individuals the speaker encountered.
Spotkałem kilku oficerów na ćwiczeniach wojskowych.
I met several officers at the military exercises.
Here, 'oficerami' is the instrumental plural form of 'oficer,' indicating a discussion the commander was having with the officers.