Abstract: A device for operation of a sliding door member, the device being movable between an open position in which the door member is open and a closed position in which the door member is closed. The device includes a pneumatic cylinder having an actuating piston and a rod assembly. A slidable cage sealingly sleeved between the cylinder and the piston reduces the force applied to the piston rod when approaching the open position. When moving towards the first position force is provided initially by conjoined movement of the piston and said cage, and finally by the piston only. A latch for locking the device in the closed position is provided by a spear secured to the piston and rod assembly and a pin to lock the spear disposed in the cylinder. A manual delatching can be achieved by a cable operated spool which moves the pin to unlock the spear.