WMG / What If…? S1E1 "What If… Captain Carter Were the First Avenger?"

The Mark I Iron Man suit was based, at least in part, on unused plans for the Hydra Stomper

Though it was clearly never built in his timeline, at some point our Tony Stark discovered plans for it among his father's things, eventually inspiring him to create the first iteration of the Iron Man armor after being kidnapped and locked in a cave by the Ten Rings.