The most common and most likely answer to this crossword clue is the 12 letter word TRANSPACIFIC
I've seen this crossword clue in The Times
T
R
A
N
S
P
A
C
I
F
I
C
More clues leading to the result TRANSPACIFIC
Buddy explains!

The straight part
We know that "Crossing ocean" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crossing ocean = transpacific.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.