1. IN A ROCKET-TYPE, THE COMBINATION OF A TUBULAR BODY HAVING A SIDE WALL WITH INNER AND OUTER SURFACES AND PROVIDED IN SAID SIDE WALL WITH A SLOT, AND NON-YIELDABLE BUT RELEASABLE MEANS FOR ANCHORING SAID BODY TO THE GROUND TO FACILITAE DEVELOPMENT OF SUBSTANTIAL ROCKET THRUST PRIOR TO TAKE-OFF, SAID MEANS COMPRISING A HOOK PIVOTALLY MOUNTED IN SAID SLOT AND SWINGABLE FROM A PROJECTED POSITION WHEREIN IT PROTRUDES OUTWARDLY BEYOND THE OUTER SURFACE OF SAID SIDE WALL TO A RETRACTED POSITION WHEREIN IT IS DRAWN FULLY INTO THE SLOT, AN ANCHORING CABLE SECURED AT ONE END THEREOF TO THE GROUND AND PROVIDED AT ITS OTHER END WITH AN EYE, SAID EYE BEING CONNECTED TO SAID HOOK WHEN THE THE LATTER IS PROJECTED AND BEING ENGAGEABLE WITH THE OUTER SURFACE OF SAID SIDE WALL TO SLIDABLE WITHDRAW SAID HOOK FROM THE EYE AND THUS SEPARATE SAID CABLE FROM THE HOOK WHEN THE LATTER IS RETRACTED, A ROTATABLE LOCKING RING MOUNTED IN SAID TUBULAR BODY AND HAVING ITS OUTER MARGINAL EDGE IN CONTACT WITH THE INNER SURFACE OF SAID SIDE WALL, SAID RING BEING DISPOSED AND ROTTABLE IN A TRANSVERSE PLANE OF SAID BODY, SAID HOOK ABUTTING SAID OUTER MARGINAL EDGE OF SAID RING WHEN THE HOOK IS PROJECTED WHEREBY TO LOCK THE HOOK AGAINST MOVEMENT TO ITS RETRACTED POSITION, THE OUTER MARGINAL EDGE PORTION OF SAID RING BEING PROVIDED WITH A NOTCH FOR RECEIVING SAID HOOK IN THE RETRACTED POSITION OF THE LATTER WHEN SAID LOCKING RING IS ROTATED IN SAID BODY TO AN UNLOCKED POSITION WHEREIN SAID NOTCH IS IN RADIAL ALIGNMENT WITH SAID HOOK, MEANS IN SAID BODY FOR ROTATING SAID LOCKING RING, AND MEANS DISPOSED WHOLLY WITHIN SAID BODY FOR RETRACTING SAID HOOK INTO SAID NOTCH UPON ROTATION OF THE RING TO ITS UNLOCKED POSITION.