This study explores the ASTOVL aircraft project design work undertaken by two groups, based at Kingston and Warton in the UK, during the period 1957-1988. ASTOVL aircraft are defined as supersonic V/STOL combat aircraft - essentially successors to the P.1127/Harrier series of 'jump jets'. Project design is taken to be the design activities preceding a full commitment to a project launch, including related government-based procurement and research activities. The relationship between project design and other stages in aircraft development in defence procurement is also looked at. A qualitative longitudinal study is the main methodological approach taken, with two periods, 1960-65 and 1980-85, the main focus of the study. The research is based on wide ranging interviews with key participants from industry and government, as well as extensive archive research. A review of the relevant literature is made, as well as being utilised as secondary source material. Two models, derived from the empirical work, are used as a basis for analysis. Contemporary and international relevance is provided by conclusions that link the work to the current JSF project, as well as linking to project design in other sectors and to activities such as systems engineering. The research is original in looking at the design activities inside a defence company at the start of the procurement process. The main contribution of the D.Phil is in showing that persistent differences between how two design teams work have implications for our understanding of how defence procurement functions.