The most common and most likely answer to this crossword clue is the 14 letter word SUBLIEUTENANCY
I've seen this crossword clue in The Times
S
U
B
L
I
E
U
T
E
N
A
N
C
Y
Buddy explains!
The straight part
We know that "Position of junior officer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case position of junior officer = sublieutenancy.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.