Combustion supporting air in the resonator tube of a pulse jet engine is cyclically compressed by combustion and discharged through a decelerating passage of a diffuser in a tail section of the engine to internally pressurize an afterbody preceding atmospheric dishcarge of the combustion products through nozzle passages, followed by primary refill with air from the pressurized afterbody and secondary refill by reentry of external air. The nozzle passages are formed in angularly spaced, rearwardly diverging vane formations of the tail section projecting from a protective casing directing ram air intake into orifice openings formed in a rear end portion of the diffuser to regulate afterbody pressurization under control of ram pressure created by forward propulsion of the engine.