This is the 265th most frequent Russian word.
военного
"Военного" means "military" or "of the military" in English.
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.
Ему нужно было услышать совет военного.
He needed to hear the advice of a military expert.
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.