A cock on a dung hill sees a bull he wants to kill. He raises a navy and impresses ducks for a crew. He would lead the attack but his hen fears he'd be killed. His courage fails and he stays home but sends the ducks to fight John Bull.
Moylan: "The Cock is France, or perhaps Napoleon, and the Bull is England." - BS
The meaning depends much on the exact dating of the song, I think. After General Hoche's invasion of Ireland failed (for which see, e.g., "The Shan Van Vogt"), Napoleon twice contemplated amphibious action against Britain. In 1798, he considered invading Ireland -- but instead went to Egypt, leaving only a few ships and soldiers to sail for Ireland; they arrived after the 1798 rebellion had failed and accomplished very little.
In 1804-1805, Napoleon went for bigger things: He was going to invade England itself, and built up his forces dramatically. But then he headed east to fight the Third Coalition, leaving his fleet to be beaten at Trafalgar.
Either dating fits the events in the song, obviously, but all those impresseed ducks sound more like the inexperienced French navy of Trafalgar. The navy of 1798 wasn't any better, but it didn't send so many involuntary sailors to Ireland.
William Ball was a writer of humorous verse about Irish history; in this index, see "Cockledemoy (The French Invasion)," "Do as They Do in France," "The Dying Rebel," and "Faithless Boney (The Croppies' Complaint)" -- though he doesn't seem to have made much impression on the wider world of literature; I have been unable to find any of his writings in any of my literary references. - RBW