Using 30 μm Pt and Pt 13 per cent Rh thermocouples, flame temperatures of uncatalysed and catalysed ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) composite solid propellants were measured under subatmospheric conditions. Ferric oxide Fe2O3 and copper chromite (CC) were the catalysts used. The study demonstrates that Fe2O3 catalysed propellant, notwithstanding its least combustion efficiency under subatmospheric conditions and weak gas-phase flame, has the maximum burning rate enhancement. This is argued to be due to the increased surface and subsurface reactions caused by Fe2O3. CC-catalysed propellant burns to the least subatmospheric pressure with minimum loss in combustion efficiency indicating that this class of propellant may be more suitable for base-bleed applications.