1. IN A PRESSURIZED GAS OPERATED CIRCUIT BREAKER, THE COMBINATION COMPRISING AN ELONGATED TANK CONTAINING A SUPPLY OF PRESSURIZED GAS, A FIRST HOLLOW INSULATOR COLUMN UPSTANDING ON SAID GAS SUPPLY TANK AND HAVING ITS INTERIOR IN COMMUNICATION WITH THE INTERIOR OF SAID GAS SUPPLY TANK, AN INTERRUPTER CHAMBER LOCATED AT THE UPPER END OF SAID INSULATOR COLUMN, PRESSURE GAS OPERATED LOAD INTERRUPTER CONTACT MEANS WITHIN SAID INTERRUPTE CHAMBER, AN OPERATING VALVE AT SAID INTERRUPTER CHAMBER CONTROLLING ADMISSION OF PRESSURIZED GAS INTO SAID CHAMBER FROM THE INTERIOR OF SAID INSULATOR COLUMN TO ACTUATE SAID CONTACT MEANS, A VALVE ROD EXTENDING UPWARDLY THROUGH SAID INSULATOR COLUMN FROM THE BASE THEREOF FOR ACTUATING SAID OPERATING VALVE, ELECTRO-RESPONSIVE CONTROL VALVE MEANS, PNEUMATICALLY ACTUATED DRIVE MEANS CONNECTED TO SAID VALVE ROD AT THE BASE OF SAD INSULATOR COLUMN AND WHICH ARE CONTROLLED BY SAID CONTROL VALVE MEANS, A SECOND HOLLOW INSULATOR COLUMN UPSTANDING ON SAID GAS SUPPLY TANK, AN ISOLATOR CHAMBER LOCATED AT THE UPPER END OF AND IN COMMUNICATION WITH THE INTERIOR OF SAID SECOND INSULATOR COLUMN, PRESSURE GAS OPERATED ISOLATOR CONTACT MEANS WITHIN SAID ISOLATOR CHAMBER WITH THE INTERIOR CONTACT MEANS WITHIN SAID OF SAID ISOLATOR CHAMBER WITH THE INTERIOR OF SAID GAS SUPPLY TANK, A PNEUMO-RESPONSIVE CONTROL VALVE MEANS LOCATED AT THE BASE OF SAID SECOND INSULATOR COLUMN FOR CONTROLLING FLOW OF PRESSURIZED GAS FROM SAID GAS SUPPLY TANK TO SAID ISOLATOR CONTACT MEANS FOR ACTUATION THEREOF, CIRCUIT MEANS CONNECTING SAID LOAD INTERRUPTER CONTACT MEANS AND SAID ISOLATOR CONTACT MEANS IN SERIES BETWEEN INLET AND OUTLET TERMINALS OF SAID CIRCUIT BREAKER, A CONTROL BLOCK ON SAID GAS SUPPLY TANK, ELECTRICAL TRANSMISSION MEANS EXTENDING FROM SAID CONTROL BLOCK TO SAID ELECTRORESPONSIVE CONTROL VALVE MEANS AT SAID FIRST INSULATOR COLUMN, PNEUMATIC TRANSMISSION MEANS EXTENDING FROM SAID CONTROL BLOCK TO SAID PNEUMO-RESPONSIVE CONTROL VALVE MEANS AT SAID SECOND INSULATOR COLUMN AND AUXILIARY PNEUMATIC TRANSMISSION MEANS EXTENDING FROM SAID PNEUMATIC TRANSMISSION MEANS AT SAID CONTROL BLOCK TO AND FOR ACTUATING AUXILIARY PNEUMO-RESPONSIVE MEANS AT SAID NORMALLY ELECTRO-RESPONSIVE CONTROL VALVE MEANS TO ACTUATE THE LATTER IN THE EVENT OF A FAILURE OF THE NORMALLY OPERATIVE ELECTRORESPONSIVE MEANS.