A self-locking plug, for use in the recovery of a pipeline laid on a deep submerged bed, consists of the combination of a cylindrical body having a rear section for insertion into the submerged end of the pipeline to be recovered and an ogival front end containing an exhaust port, an exhaust pipe extending along the axis of the cylindrical body from its rear end to the exhaust port, an exhaust valve, locking shoes carried by the cylindrical body, a plastic sealing ring carried in an outer groove in the cylindrical body, and means simultaneously actuated by compressed fluid carried in the ogival front end of the cylindrical body to press the locking shoes against the inner wall of the pipeline and fasten the plug to it and to force the sealing ring against the inner wall of the pipeline and prevent the flow of water around the cylindrical body.