Comics #5 (Summer 1942).
Golden Age Appearance: USA Comics #5.
Modern Appearance: None.
Dates Active: 1942-?
The Blue Blade was a hero who dressed like a bare-chested Musketeer, rode a horse, was good with his fists, and presumably was good with his sword, although he didn't use it in his only appearance. No origin was given for the Blade, although it was established in his only appearance that he was working on the Pacific Coast of the U.S., after having ridden across the country to get there.
Note: Contrary to what Jerry Bails and Howard Keltner say, there is NO evidence, none, zero, zippo, nada, nihil, within the actual stories themselves that the Fourth Musketeer and the Blue Blade were the same character. The only thing they have in common is that they both have a general Musketeer theme, but other than that the characterisation, costumes, and backgrounds (such as they are) are different. However, with that said I have to admit that there does seem to be some (purely external) evidence that the Blade might have been the Musketeer renamed. What I find persuasive is the lettering in the panels in which the Blade's name is used. It looks, to my eyes, like the panels have been relettered, with "Fourth Musketeer" whited out or erased and "Blue Blade" inserted. Still and all, though, they have different names and should be treated as different characters.