A tailcone assembly for an undersea vehicle includes a first tailcone portion having a cavity and a second tailcone portion positionable in and axially extensible from the cavity. An extensible drive shaft is provided for joining the vehicle's engine to a propeller. The extensible drive shaft includes a first drive shaft joined to the engine, and a second drive shaft rotating with the first drive shaft. The second drive shaft is supported by the second tailcone portion and is axially extensible from the first drive shaft upon deployment of the second portion. The propeller is positioned on the second drive shaft outside the second portion. A biasing means is provided between the tailcone portions for deploying the second portion.