A few examples of the military use of unmanned systems dates back well over a century; however, the development accelerated during World War I and II. The early use of these systems included use as target platforms, surveillance and reconnaissance, as well as a platform for bringing explosives towards enemy lines and platforms. The use cases have evolved since then and unmanned systems are now being used for a large number of tasks in all domains using air, ground, surface and sub-surface platforms. The report provides an overview of the development of military unmanned systems, and provides some reflections and lessons-learned that can influence the current development. The focus of the report is on the historical development but some modern systems that are still in operational use are also described briefly.