The Black Knight Gamma motors.
The early Black Knights used the Gamma 201 motor. This had a thrust of 16,400lb at sea level.
Later BKs used the 301, which had new chambers and a much improved fuel/oxidant mixture control. It was capable of higher thrust, and used at 21,600lb thrust on later launches. The chamber came from the Stentor motor developed for Blue Steel by Armstring Siddeley.
Another view of the 301: it shows clearly how the chamber was made of thin tubes brazed together and formed to the shape of the chamber. There are re-inforcing bands around the chamber for strength.