1. A safety and arming device for an orDnance comprising: fluid pressure operated means for changing from a first position to a second position under the influence of fluid pressure above a predetermined magnitude; biasing means acting on said fluid pressure operated means in opposition to the fluid pressure for returning said fluid pressure operated means to a first position when the fluid pressure decreases below a predetermined magnitude; arming means movable between an unarmed position wherein an explosive train to the ordnance is interrupted and an armed position wherein the explosive train to the ordnance is complete; and transmission means connecting said fluid pressure operated means to said arming for causing movement of said arming means from an unarmed position to an armed position when said fluid pressure operated means changes from the first position to the second position under influence of fluid pressure above said predetermined magnitude and for returning said arming means to an unarmed position when said fluid pressure operated means is returned to the first position; and switch means coupled to said first fluid pressure operated means for establishing electrical contact between a delivery vehicle and an ordnance only while said fluid pressure operated means is located in the second position.