The most common and most likely answer to this crossword clue is the 2 plus 6 plus 7 letter word ON ACTIVE SERVICE
I've seen this crossword clue in The Daily Telegraph
O
N
A
C
T
I
V
E
S
E
R
V
I
C
E
Buddy explains!
The straight part
We know that "in the navy, maybe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in the navy, maybe = on active service.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.