Click on the city building without opening the city menu like if you want to shoot with it.
There is the gaus pylon button.

Thanks for the information. Bought it on gog as well.

So better not installing and waiting for 1.3.3 ?

It‘s an invasion! No easy kill some units here and there. Keep your head up. The waves are getting tougher, but when you fend off the last tesseract vaults, you will claim the victory!

(Did it today, lost half my cities)