The more Steam Points you expend in the Steam Gun, the higher the pressure of the resultant gout of steam. If the Steam Tank is unengaged, declare how many Steam Points you will expend in the Steam Gun at the start of your Shooting phase. If the Steam Tank is engaged in close combat, declare how many Steam Points you will expend in the Steam Gun at the start of your Close Combat phase. In either case, if you choose not to expend any Steam Points in the Steam Gun, you cannot fire it that turn.

If only a single Steam Point is expended, the Steam Gun is treated as a Strength 2 Breath Weapon, which uses the Engineer Commander's Initiative. The Strength of the Breath Weapon is increased by 1 for each additional Steam Point expended in the Steam Gun. (For example, if 3 Steam Points are expended, the Steam Gun is treated as a Strength 4 Breath Weapon.) The Steam Gun has a 360 degree arc of fire. Unlike other Breath Weapons, the Steam Gun can be used once each turn.