By 1937, Siegel & Shuster had five comic strips going in National Allied Publications / DC Comics. “Spy” debuted in Detective Comics #1, but the dynamic between Bart Regan (newly minted spy for Uncle Sam) and his ex-fiance Sally Norris started taking shape in the second issue, March 1937. Sally became Bart’s reluctant sidekick / damsel in distress while Bart tries to hide that he is now a spy.
Most of Joe Shuster’s heroes look alike: Doctor Occult, Steve Carson (Federal Men), Sandy Kean (Radio Squad), and Bart Regan (Spy) all kind resemble early Superman: slicked-back dark hair, square jaw, etc. The only standout is Slam Bradley, who had his own look (red-haired and usually shirtless).