Schwerer Gustav
The Schwerer Gustav was an 80cm railway gun of which about 2 were constructed. Requires Munitions Plant.
Built by Nazi Germany in WW2, it was around 40m long, weighed 1,350 tonnes, and fired a 7 tonne shell. It could fire said shell 30+km away. Far enough to hit London from France.
Here in forts it is just as devastating. It will cost you 5,000 metal and 10,000 energy, as well as require a massive space, and a sturdy fort. Make sure to crossbrace and build extra foundations.
Anything it hits or even misses will be instantly obliterated.
Special Thanks to SamsterBirdies for sorting out the sprite positions.