Recently, Colin Kaepernick has come under fire for protesting the playing of "The Star Spangled Banner" at football games. One recent talking point in the controversy has claimed that the original third verse of Key's anthem refers to free blacks and slaves who fought for the British Army in America. The verse, in full, is below:

And where is that band who so vauntingly swore, That the havoc of war & the battle’s confusion/ A home & a Country should leave us no more ? Their blood has wash’d out their foul footsteps’ pollution./ No refuge could save the hireling & slave From the terror of flight or the gloom of the grave,/ And the star-spangled banner in triumph doth wave O’er the land of the free & the home of the brave.

The relevant lines are "No refuge could save the hireling & slave From the terror of flight or the gloom of the grave."

However, to me, these lines refer to the Hessian mercenaries hired by the British in the American Revolution and the conscript armies fielded in the Napoleonic Wars/War of 1812. Hireling can refer to a free black hired for labor (it can refer to any hired, low-wage laborer or immigrant) but in this case it seems like a diminutive term used to disparage the British Army. Slave almost certainly refers to conscripts, as the British Army fielded thousands of them in America during the War of 1812.