A39 Tortoise gun on tow

The Tortoise heavy assault tank (A39) was a British heavy assault gun design developed during the Second World War, but never put into mass production. It was developed for the task of clearing heavily fortified areas such as the Siegfried Line and as a result favoured armour protection over mobility.

Although heavy, at 78 tons, and not readily transported, it was considered reliable and a good gun platform.

Only a few prototypes of the Tortoise had been produced by the end of the war.
https://en.wikipedia.org/wiki/Tortoise_heavy_assault_tank

The same image from a different vantage point:

The A39 Tortoise being towed on an 80-ton trailer by two Diamond T's during trials in BAOR, 1948