Abstract: There is provided a propulsion unit that is incorporated in an endoscope or borescope. Advancement of the insertion tube through a passageway is attained by a series of washers or similar members that can be mounted on the insertion tube of the borescope and can independently move coaxially with respect to the insertion tube. When the tube is passed into a passageway, the washers contact the walls. A drive motor that is associated with the insertion tube axially reciprocates the washers and transmits the axial motion to the insertion tube. The rate of movement of the washers is nonuniform and washer movements are phased such that at any point in time more washers are moving in one direction than in the opposite direction. The resultant frictional forces are such that net forward motion of the tube is achieved.