This report documents the experiments made and results obtained in a study to investigate the effects of hardening epoxy-carbon fibre composites under hydrostatic pressure of 100 bar. A method has been developed for hardening fibre composites under high pressures, and the method has been successfully applied to processing small samples. These samples have been mechanically tested and compared to similar materials hardened under conventional pressures. High-pressure hardened materials show reduced porosity and lower levels of inter-laminar matrix. The interlaminar shear strength (ILSS) is only slightly improved, but it is noteworthy that scatter was reduced by 50%. However, an insufficient number of samples were tested. It appears that hardening under high pressure does lead to some improvement in strength of carbon-fibre composites, which may be useful in military applications.