No song should need Cole`s Notes to follow... but if folks can write zillions of words on the forum about stuff like bumping posts, I feel justified in providing a few unnescessary asides for the lyrics here ( which tell a tale 100% fictional , entirely accurate historically, and are based on Robert Hughes excellent book on Australia`s founding, The Fatal Shore).

" grog" booze (usually Rum at that time)
"black trackers" aborigines were far and away the best
"dance upon nothing" British term for hanging- they were public so it was a popular sport to watch the dancers!
"save us from the gallows
to sail us to the moon" - most early tranportees were sentenced to hang, the sentence commuted - a few years to life in Australia, a place as distant as the moon to your average 18th century bread thief.

There... if the song is still a mystery, a better scholar than I will need to get involved.

Robert