USA T131 280mm Heavy Motorized Gun
This is the experimental model of the M65 atomic cannon. Adopted in 1956, the cannon could fire both nuclear and conventional shells up to 18 miles. The cannon weighs 47 tons and is mobile. The prime mover consists of both a front and a rear truck that can reach a maximum speed of 30 mph. The atomic cannon was replaced by more mobile rockets in the mid 1960s.


Think that’s bad? Check out the Davy Crockett Nuke
https://en.wikipedia.org/wiki/Davy_Crockett_(nuclear_device)
The M388 could be launched from either of two launchers known as the Davy Crockett Weapon System(s): the 120 mm (4.7 in) M28, with a range of about 1.25 miles (2.01 km), or the 155 mm (6.1 in) M29, with a range of 2.5 miles (4.0 km).
Nonononono that one is called „Fat Man“ (Source: I played Fallout 3)