Rocking Chair Underwear

Henderson and Ervin and their Rocking Chair Underwear have disappeared into history, leaving only cryptic ads in their wake. I'm not exactly sure why a fellow would want a button "adjustable" flap on the side of his underwear or how it makes said britches more athletic, but apparently it had something to do with unusual range of movement and adjusting in a jiffy.

The ad comes from the July 1918 issue of Metropolitan Magazine and has the boot camp imagery associated with most World War I era magazine ads.