https://en.wikipedia.org/wiki/M3_Lee

The design was unusual because the main weapon – a larger caliber, medium-velocity 75 mm gun – was in an offset sponson mounted in the hull with limited traverse. The sponson mount was necessary because, at the time, American tank plants did not have the design experience necessary to make a gun turret capable of holding a 75 mm weapon.

M3s and other early American tanks are fucking weird

The Tank Museum channel on YT has really good information on tanks like this one. They explain each tank in depth with dry British humor. I fell madly in love with one of their 70-80 year old curators who was adorably frank about everything.