The T42 Medium Tank was the first prototype version of the M47 Patton. It was to be a more armored vehicle with the same firepower as the M46 Patton. The vehicle used a different hull than the M46 and the familiar turret that was used on the M47. The vehicle however was deemed unsuccessful as it had multiple issues and never made it to mass production while the turret was placed onto a modified M46 Patton hull as the Korean war had broke out and the US wasn't going to wait for the issues with the Hull to be sorted out. That tank eventually became what is known now as the M47 Patton II

The Hull of the vehicle was later used as the chassis for the T69 Medium Tank which was an experimental vehicle using a 90mm 9 round drum autoloader and an oscillating turret.