Various examples of a high-speed omnidirectional fully-actuated underwater propulsion mechanism are described. In one example, a propulsion system includes two decoupled counter-rotating rotors centered on a main axis, with each rotor comprising a plurality of pivotable blades projecting radially from the main axis, a servo-swashplate actuation mechanism comprising a plurality of servos and a linkage assembly connected from the servos to the pivotable blades, a blade-axis re-enforcing flap adapter comprising a plurality of stationary flaps, with the blade-axis re-enforcing flap adapter being positioned in a region between the two decoupled counter-rotating rotors centered on the main axis, and a controller. The controller can be configured to calculate control parameters, compensate a first control parameter among the control parameters to reduce cross-coupling of an unwanted force generated by drag forces on the two decoupled counter-rotating rotors, and generate a control signal for each of the servos based on the control parameters.