The air-blast high-voltage circuit breaker has been developed and applied on high-voltage systems of 150 and 240 kv. Both single-phase and three-phase automatic high-speed reclosing can be carried out with this new type of circuit breaker. The principles of design and operation are explained and the construction of two high-voltage air-blast circuit breakers rated at 150 kv and 220 kv, installed in Canadian power-distribution plants, is described and supplemented by a discussion of performance tests and oscillograms. The construction of an air-blast circuit breaker with axial blast, designed for extremely high voltage and high interrupting capacity, is explained, and results of various tests discussed.