Cannot seem to get either one to activate, unless I am missing something.

I can't remember which of the two Howitzers that was one of them should shoot automatically which unfortunately doesn't work and the other one needs some kind of remote control where you can click and there she shoots.
Since I don't have Factorio open right now, I can't tell you which Hauwitzer was what but I think the experimental was the one with the remote control.

Sry for Error i use translator

So use a remote control for the experimental one, got it. Thanks for the tip.

The normal Howitzer is not work we have not found the Problem