A considerable amount of research effort has, and continues to be invested into technologies and algorithms for capabilities which are forecast to be needed in future uninhabited vehicles. Much of this research is conducted with the aim of increasing the level of autonomy of these vehicles. However these technologies and capabilities provide only a part of the total system solution and must be integrated into an architecture that covers the entire vehicle system. This total system approach is particularly relevant since this is how airworthiness regulators consider Uninhabited Aircraft Systems. Airworthiness of uninhabited aircraft has been addressed by Australian aviation regulators. While the regulations may be in place, technical challenges still remain for the suppliers of these systems. For example, one of these unresolved technical challenges is the capability of uninhabited aircraft to

Uninhabited Aircraft Systems (UAS), as a relatively novel technology, was always seen as a tool available and utilized only by rich and developed states. But thanks to globalizations and the fast proliferation of commercially available drones, this platform has already been used by smaller states and also non-state groups, giving them possibilities never seen before. Yet, there is little research on how and why these new actors use UAS to claim their cause. The research question to guide this thesis is how and why do non-state armed groups differ from states when using Uninhabited Aircraft Systems in their military operations? The thesis uses a demand- and supply-side theory, adapted for the proliferation of drones to help answer that question. This theory is tested in a multiple case study involving the United States as a state and the Houthis as a non-state group during the Yemeni crisis, from 2011 to 2022. Through a structured, focused comparison between the cases, indicators from the demand- and supply-side models were used to understand the differences in drone use between different actors. The main findings are that states and non-state armed groups differ in their use of UAS mainly because they have different boundaries (legal and technological), but also for the symbol and status that this platform carries. Finally, it was seen that the theory is not only able to clarify the trends on proliferation, but also the why actors use UAS, with few remarks, but with a need to test it further.