The military aspects of hydrogeology can be categorized into five main fields: the use of groundwater to provide a water supply for combatants and to sustain the infrastructure and defence establishments supporting them; the influence of near-surface water as a hazard affecting mobility, tunnelling and the placing and detection of mines; contamination arising from the testing, use and disposal of munitions and hazardous chemicals; training, research and technology transfer; and groundwater use as a potential source of conflict. In both World Wars, US and German forces were able to deploy trained hydrogeologists to address such problems, but the prevailing attitude to applied geology in Britain led to the use of only a few, talented individuals, who gained relevant experience as their military service progressed. Prior to World War II, existing techniques were generally adapted for military use. Significant advances were made in some fields, notably in the use of Norton tube wells (widely known as Abyssinian wells after their successful use in the Abyssinian War of 1867/1868) and in the development of groundwater prospect maps. Since 1945, the need for advice in specific military sectors, including vehicle mobility, explosive threat detection and hydrological forecasting, has resulted in the growth of a group of individuals who can rightly regard themselves as military hydrogeologists.