The singer hears a sailor telling his love that he must leave her; he must go into battle. She begs him not to go. He says that he might win glory. He has fought before; he will fight again. He tears his handkerchief in two and gives her half as a token
As the titles make clear, this general text and tune were applied to whatever war seemed most convenient at the time (e.g. the Mexican War, the Civil War; a British text refers to fighting "the proud Chinee," presumably during the Opium Wars).
The Fenian version (named for the Fenians, a group of Irish-Americans who thought they could gain freedom for Ireland by invading Canada) is slightly changed; the opening is the same, but the broken token is missing, and in the end Bridget agrees that her Patrick should fight for Ireland.
The Fenians actually did purchase a ship, which they named _Erin's Hope_, but it accomplished nothing except to make one voyage to Ireland -- where no one wanted them. (For more details, see the notes to "The Cork Men and New York Men.") Similarly, they invaded Canada -- and were easily repelled, with many taken captive. Later they built a submarine; its only use was as a fundraising device.
Viewed from any standpoint except pure Irish patriotism, the Fenians were utterly ineffective and really quite silly. (For other examples, see "A Fenian Song (I)" and "The Smashing of the Van.") - RBW
Broadsides Bodleian Harding B 11(466), Firth c.12(135) and Firth b.26(180) refer to the Opium War of 1840-1842; Harding B 31(141) and Harding B 31(141) refer to the American Civil War of 1861-1865; the "William" broadsides are not specific. There are also "answers" [such as Bodleian, 2806 c.16(90), "Susan's Adventures in a British Man-of-War"] and "No. 2's" [such as LOCSinging, cw106880, "Yankee Man-of-War. No. 2." - BS