It appears to be just some mumbling and noises of war equipment, where sounds and tone of voice in itself are important (wise choice, as it would be weird to hear actual words (in what language should they be?)). But if you insist that there has to be a literal meaning, then my version would be this:
"Back, rowing, back [first voice, giving orders]... back [second voice, as if confirming]... that is [third voice, rather unclear what he's saying really]... oi! back [very weak back sound by several men]."
By the way, this little exercise reminded me the phenomenon of listening music records backward and searching for "hidden messages". It's quite hard to understand sometimes what you hear. At least I didn't pick up any "here's to my sweet Satan" phrase this time.