will also be carried by the Lockheed Martin F-35 Lightning II. B61 tactical variants are deployed with NATO allies in Europe as part of the NATO Nuclear Weapons Sharing Program. About 150 bombs are stored at six bases: Kleine Brogel in Belgium, Büchel Air Base in Germany, Aviano and Ghedi Air Base in Italy, Volkel Air Base in the Netherlands and Incirlik in Turkey. In 2012, NATO agreed to improve the capabilities of this force with the increased accuracy of the Mod 12 upgrade and the delivery of the F-35 aircraft. This added a modest standoff capability to the B61. Design The B61 is a variable yield ("dial-a-yield" colloquially) dual use tactical and strategic bomb equipped with Full Fuzing Option (FUFO) designed for external carriage by high-speed aircraft. It has a streamlined casing capable of withstanding supersonic flight. The original B61-0 weapon was long, with a diameter of and a basic weight of with most later weapons having approximately the same dimensions and weight, except for the Mod 11 version which has a weight of approximately . Ground operations The B61 is armed by ground-based personnel via an access panel located on the side of the bomb, which opens to reveal nine dials, two sockets, and a T-handle which manually triggers the "command disable" function. One of the sockets is for a MC4142 "strike enable" plug which must be inserted in order to complete critical circuits in the safety/arming and firing mechanisms. The other socket is the PAL connector, which has 23 pins marked with alphabetic letter codes. The B61 "command disable" mechanism functions as follows: after entering the correct three-digit numeric code it is then possible to turn a dial to "DI" and pull back a T-shaped handle which comes away in the user's hand. This action releases a spring-loaded firing pin which fires the percussion cap on an MC4246A thermal battery, powering it up. Electrical power from the thermal battery is sufficient to "fry" the internal circuitry of the bomb, destroying critical mechanisms without causing detonation. This makes the bomb incapable of being used. Any B61 which has had the command disable facility activated must be returned to Pantex for repair. Fuzing and delivery The B61 can be set for airburst or groundburst detonation, and freefall, retarded freefall or laydown delivery, the latter two options being achieved through the use of a parachute to slow down the weapon