Abstract: A locking device is described particularly useful for coupling a container to a crane, the locking device including a lock-pin assembly coupleable to the crane, and a slotted member fixed to the container into which member the lock-pin assembly may be inserted and then locked.The slotted member is formed with an oval slot and a square cavity underlying and communicating with the slot and having a length and width at least equal to the length of the slot. The lock-pin assembly comprises a pin, an axial-stop element fixed to the inner end of the pin, and a rotary-stop element fixed to the inner end of the pin between the axial-stop element and the outer end of the pin.