Abstract : The current focus on utilizing detonations for air-breathing propulsion has shifted from long-term studies of the possibility of fuel energy transformation in stabilized oblique detonation waves to investigations and practical development of propulsion engines operating on propagating detonations in a pulse mode. Contrary to the oblique-detonation concept that is applicable to hypersonic flight at velocities comparable or higher than the Chapman-Jouguet detonation velocity of the fuel-air mixture, the concept of a pulse detonation engine (PDE) is attractive for both subsonic and supersonic flight with the PDE as a main propulsion unit or as an afterburner in turbojet or turbofan propulsion system. In particular, PDE-based propulsion is attractive for flight Mach number up to about 4. Within this range of Mach number, solid rocket motors are known to be very efficient in terms of simplicity and high-speed capability, but they have a limited powered range. Turbojet and turbofan engines, due to their high specific impulse, provide longer range and heavier payloads, but at flight Mach number exceeding 2-3, they get too expensive. Ramjets and ducted rockets designed for flight Mach number up to 4 require solid rocket boosters to accelerate them to the ramjet take over speed, which increase the complexity and volume of a propulsion system. Combined-cycle engines, such as turborockets or turboramjets, are also very complex and expensive for similar applications.