In a missile launching apparatus in which a missile is coupled to a launching rack by an umbilical cord which passes through an opening in the skin or fairing of the missile, there is provided a device for severing the umbilical cord. This device includes a rotatable disk provided wth a hole which is offset relative to the axis of rotation of the disk and through which hole the cord passes. A cable is provided connecting the disk with the launching rack so that upon launching, the disk is rotated through a fraction of a turn. The disk is provided with a knife edge bordering part of the aforementioned hole for purposes of severing the umbilical cord. The hole in the disk is provided in a half of the disk and the other half of the disk is at least substantially imperforate. This latter half of the disk operates to obturate the opening in the skin of the missile after the umbilical cord has been severed. A safety pin is provided to lock the disk against rotation prior to launching of the missile and this pin is of a strength to be sheared when the disk is rotated by the aforesaid cable. In addition, there may be provided a switch which includes an actuator bearing against the disk and adapted to enter the aforesaid hole upon rotation of the disk in order to actuate the switch.