The most common and most likely answer to this crossword clue is the 6 letter word SMYRNA
S
M
Y
R
N
A
More clues leading to the result SMYRNA
- Old port — the writer’s joining British sailors in it
- Rampaging army’s capturing any number in ancient city
- Army’s beaten, defending northern city of old
- Old port? Gosh, our navy has docked in it!
- Southern army deployed around new Mediterranean port
- Fig variety in Atlanta suburb
- Southern army manoeuvres involve Navy in Turkish port
Buddy explains!

The straight part
We know that "Old port" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old port = smyrna.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.