Today, system availability is a determining factor in system deployment because it must be guaranteed in the operational phase while taking a large part of assets whole life cycle cost (WLCC). Thus, controlling system availability is now a critical issue in systems engineering. This is even more true for military systems that operate in a battle context. In fact, since they must act in a hostile environment, they can become unavailable due to system failures or damage. In both cases, it is necessary to regenerate the system in order to restore its availability in mission. In this paper, we propose a weapon system modelling method that supports regeneration engineering. This method relies on a unified failure/damage approach to extend accepted availability models. It integrates both failures and damage, as well as the possibility of regeneration, into the operational availability assessment. The proposed method is illustrated with an example of weapons system architecture.