It’s time again to reveal some more secret information that was hinted at in the last dev diary. Specifically, this week will be revolving around the final part of railways and trains.
So to start off we'll go through how you get a railway gun on the map because it’s a little different from normal land units. First of all, you are going to want to research railway guns which come after armored trains. Then you can find it in your production tab just like building normal equipment. But unlike other equipment you build, these production lines are limited to 5 factories and the railway gun won't be added to your stockpile. Instead, once completed, your brand new railway gun will appear in your capital, in this way they are built similar to capital ships.
Moving your railway gun is limited to provinces with railways, and so to get to the front you must have a rail connection. Taking into account the rail conversion time when capturing territory is important as you will have to wait for the big guns to be able to help you out.
You can also attach railway guns to armies just like with planes and they will attempt to place themselves relative to the frontline. If you have several, they will be distributed where possible to support your army. There is also a quick-select button on the army to select all railways guns attached to an army should you need to.
Finally, the last bit of control understanding is range. Railway guns have a range in which they can support and so from any one point are limited in which provinces they can support. This range is shown by hovering over the unit icon.