An inline variable sonic valve is provided that includes a housing defining an inlet and an outlet positioned inline along a gas flow axis. A contoured metering plug is fixed within the housing and a diverging sleeve is movably positioned within the housing downstream of the contoured metering plug. An actuator is positioned offline from the gas flow axis and is configured to move the diverging sleeve within the housing relative to the contoured metering plug fixed therein to vary a gas metering area defined between the contoured metering plug and the diverging sleeve. The actuator may be hydraulic, fueldraulic, pneumatic, or electric, and may drive the diverging sleeve discretely to an open or a closed position, or to a variable position between the open and closed position when a position senor is included to meter the flow therethrough.