Jimmy Martin was born in the mid-to-late 1920's in suburban New York.  He lived with his mother and brother, until the older brother found employment in a local factory exploiting child labor. The older brother Billy succumbed to relentless labor in the factory but the owner, Tareff, has is declared heart failure.  Being the 12th child to suddenly die of heart failure attracts the attention of Hourman, who visits Billy's family.  There, younger brother Jimmy fills in the hero about conditions inside the factory and his suspicions about the fate of his brother,  Hourman investigates, ultimately coercing Tareff to sign over his factory and leave town.  Impressed by Jimmy's amateur radio operations, Hourman suggested that his network of ham radio operators form a club to assist him fight crime, to which Jimmy quickly agrees.  The group becomes known as the Minute-Men of America (Adventure Comics #53).

The group is immediately successful with hundreds of members around the nation.  Jimmy becomes "Captain Martin" or alternatively, Minute-Man.  Initially, Jimmy acts as a coordinator and occasionally gets involved in direct case work.  Examples include rescuing fellow member Rodney Morvan when he is kidnapped by criminals targeting his banker parents (Adventure Comics #54), thwarting criminals who exploit a kids leadership day (Adventure Comics #55) and defeated a gang of kids impresonating them (Adventure Comics #60).

Over time, Hourman's case work became more dangerous with rise of villains like Dr. Togg, Dr. Darkk and Dr, Iker.   Jimmy and the Minute-Men still server as look-out and co-betweens but rarely entered the fray with the monsters and robots these criminal deployed.  Jimmy craved a larger piece of the action and in 1942, convinced Hourman to let him join him as a costumed sidekick.  The two tangled with defeated Professor Q, with the criminal falling to his apparent death (Adventure Comics #73).  Almost immediately thereafter. Jimmy's mother took him and left town with telling Hourman, leaving Thorndyke Thompkins in charge of the Minute Men (Adventure Comics #74).  The ultimate fate of Jimmy Martin on Earth-Two has not been revealed.