Black Arrow's engines had a very remarkable design. For booster stages on space rockets you really need some sort of pump to get a high enough chamber pressure

Black Arrow's engines had a very remarkable design. For booster stages on space rockets you really need some sort of pump to get a high enough chamber pressure. Most rockets due this by burning some of the fuel and oxidizer in a turbine, wasting a bit of fuel. What Black Arrow did was use the decomposition of the high test peroxide to power the pump and then putting all of the result into the combustion chamber. Sort of like a staged combustion engine but developed much earlier. You'll always have worse efficiency with peroxide than with liquid oxygen but it was some very clever engineering.