> OPPO
> Naval slang - short for opposite number - for the person doing the same job as one's self in another watch or ship. In the former case, since you relieved each other (in the old two-watch days), it behoved you to become friends; thus the word Oppo came to mean Chum. On a two-watch watchbill, the name of a man's 'opposite number' in the other watch was shewn against his own name in the opposite column.
https://www.hmsrichmond.org/dict_o.htm https://en.wiktionary.org/wiki/Appendix:Australian_English_m...
> OPPO > Naval slang - short for opposite number - for the person doing the same job as one's self in another watch or ship. In the former case, since you relieved each other (in the old two-watch days), it behoved you to become friends; thus the word Oppo came to mean Chum. On a two-watch watchbill, the name of a man's 'opposite number' in the other watch was shewn against his own name in the opposite column.