AbstractSimulation of air-defence engagements between ground forces and aircraft or helicopters requires complex models to examine the many-on-many interactions. One of the critical factors determining the outcome of a low-altitude engagement is the terrain over which it is fought. The terrain determines the aircraft's flight path as well as the firing opportunities for the ground forces. Methods of terrain representation that work well for aircraft engagements may not be suitable for helicopters. The different flight characteristics of helicopters cause them to interact more closely with microterrain features and so modify their flight paths. Representation of microterrain features on the terrain database leads to significantly different exposure statistics compared with those obtained when such features are absent. A bias is also present in battle-simulation results, leading to the conclusion that microterrain must be included to obtain realistic battle-model outputs when studying air defence against helicopters.