The most common and most likely answer to this crossword clue is the 9 letter word SUBALTERN
I've seen this crossword clue in The Guardian
S
U
B
A
L
T
E
R
N
More clues leading to the result SUBALTERN
- Captain's junior is to change name on boat
- Junior officer's payment to change name
- Junior officer in navy, on vessel working late
- Inferior doctor has name at the bottom of roll
- Officer learns but gets confused
- Unstable suspect cornering Republican soldier
- Officer getting vessel to change direction
- Young army chap is awkward, but learns
- Officer is a star, beginning to bring change internally
- Officer to get boat and change direction
Buddy explains!

The straight part
We know that "Young army chap" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case young army chap = subaltern.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.
What does SUBALTERN mean?
SUBALTERN noun- A subordinate.
- A commissioned officer having a rank below that of captain; a lieutenant or second lieutenant.
- A subaltern proposition; a proposition implied by a universal proposition. For example, some crows are black is a subaltern of all crows are black.
- (literary theory) A member of a group that is socially, politically and geographically outside of the hegemonic power structure of the colony and of the colonial homeland.
- Of a lower rank or position; inferior or secondary; especially ranking as a junior officer, below the rank of captain.
- Asserting only a part of what is asserted in a related proposition.