A rotary ram compressor for use in gas turbine engines and the like, having a plurality of vanes attached to discs, with the opposing parts of each two adjacent vanes and the opposing parts of the disks' surfaces confined between the opposing parts of the surfaces of the two adjacent vanes defining a channel in-between. Each channel is formed of two successive freely communicating portions: a first diverging inlet portion; and a second constant cross-sectional area outlet portion. In operation, gases are rammed into the first diverging inlet portion of the channel and are gradually displaced to the second constant cross-sectional area outlet portion of the channel, while being diverged, resulting into a rise in the static pressure energy of the gases, followed by smoothening of the stream of flow of the pressurized gases within the second constant cross-sectional area outlet portion of the channel.