This is the 265th most frequent Russian word.
военного
"Военного" means "military" or "of the military" in English.
The word 'военного' here refers to its genitive form, indicating belonging or relation to a military person, used in the context of 'memoirs of' a soldier or veteran.
Он читал мемуары военного.
He was reading the memoirs of a military person.
Here, 'военного' in the genitive denotes belongings, specifically of a soldier or a military personnel individual.
В музее представлены личные вещи военного.
The museum displays personal belongings of a soldier.
In this sentence, 'военного' is again in the genitive case, used to show that the advice comes from a person with expertise in military matters.