The most common and most likely answer to this crossword clue is the 10 letter word MAN-OF-WAR
I've seen this crossword clue in Financial Times
M
A
N
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O
F
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W
A
R
More clues leading to the result MAN-OF-WAR
Buddy explains!
The straight part
We know that "old ship" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old ship = man-of-war.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 MAN-OF-WAR mean?
MAN-OF-WAR noun- An armed naval vessel, primarily one armed with cannon and propelled by sails.
- A jellyfish-like marine cnidarian of the family Physaliidae, a Portuguese man-of-war or Pacific man-of-war.
- A man of war bird, a magnificent frigatebird.