This paper presents an agent-based model to compare different coordination patterns in joint fire support (JFS) scenarios. Modern war fighting approaches depend heavily on a separation of concerns (like reconnaissance, coordination and engagement) and therefore impose high requirements on the coordination of all involved parties. Following the General Reference Model for Agent-Based Modeling and Simulation (GRAMS), we present an agent-based model of this problem domain. Our simulations indicate that decentralized JFS coordination leads to smaller average times from identification of a target to final engagement, while at the same time requiring extensive resources. Central coordination is more effective in terms of engaged units and reduced resource requirements, but tends to take more time.