Hellcanons?

Is there any way to 'activate' hell cannons?

When I order them to shoot at an enemy, they say "Atta-Ready for orders" and don't fire at all.

They just stand there, waiting to get slaughtered, even if it say's they're firing ranged missles, they don't.

Any way to fix this?

Cheers.

EDIT: It seems there is a problem with the range. The cannon thinks the target is in range, even when it's not.