This is the 10655th most frequent Korean word.
군대에
"군대에" means "to the military."
Here, "군대에" expresses the location where the subject was situated during the mentioned time.
그는 군대에 있는 동안 가족을 자주 생각했어요.
While he was in the military, he often thought of his family.
The phrase "군대에" is used to indicate the destination or place connected to the action, in this case, 'going to the army'.
사촌이 군대에 간다고 들었어요.
I heard that my cousin is going to the army.
In this context, "군대에" denotes the location or institution the subject considers joining or going to.