Nether-shirt

And not content with imparting this valuable information to the public, the editor of the great daily publishes the results of his investigations into the probable cost of a nether-shirt of such fine material, [...]

Because the men did not have uniforms, they presented a crazy quilt array of dress. "Many were shirtless, except the nether shirt, shoeless, hatless, and pantless — in fact, were quite 'less' in every way," Charles Hopkins noted.