The Fench (and also the Russian) had real artillery corps. This unit represents the concentration of heavy pieces that sometimes was used (more and more as the war progressed). They are immobile except that, when activated and when there is no enemy unit in contact, you may (mount) them. While mounted, they cannot fire at all. each turn they may be move 1 hex just like ordering a unit. When they have reached their destination, you may order them to 'unlimber'. The turn after they can fight again. Note that gun postions do not move with them.