Embodiments generally relate to propulsion tube units and propulsion devices for progressing instruments along passages, and associated methods of use. For example, the instruments may include, tools, sensors, probes and/or monitoring equipment for medical use (such as endoscopy) or industrial use (such as mining). In some embodiments, the propulsion device may comprise an elongate tube defining a channel configured to accommodate a liquid and a pressure actuator in communication with the channel. The pressure actuator may be configured to selectively adjust a pressure of the liquid in the channel to alternatingly: reduce the pressure to induce cavitation and form gas bubbles in the liquid； and increase the pressure to collapse some or all of the gas bubbles back into the liquid, thereby accelerating at least part of the liquid towards the first end of the tube and transferring momentum to the tube to progress the tube along the passage.
