The earliest forms of jet-propulsion, such as the pulse jet utilized in the Flying Bomb, were incapable of functioning at rest, in view of the absence of any means of air-compression.

• 早期的一些类型的喷气推进器，诸如飞弹所用的脉动式喷气发动机，由于没有任何空气压缩手段而在静止状态下就不具有推进功能。