commanders during the Sơn Tây raid. For more information on serial numbering of military aircraft, see United States military aircraft serial numbers. Rockets/missiles Status prefix Status prefix is an optional prefix not always used for vehicles in regular service. If used, it is the first letter in the MDS. Authorized current status prefixes are: e Digitally developed. Vehicles that are developed in a digital environment. C Captive. Only used for rockets and missiles, C applies to rockets/missiles that are designed to be carried in their launch environment but are incapable of being launched/fired. They may contain guidance and control electronics but the engine and warhead are typically inert or ballasted. D Dummy. Only used for rockets and missiles which are non-flying, primarily for ground training. All guidance, control electronics, engine, and warhead are inert or ballasted. J Temporary Special Test. Applied to craft involved with special testing of temporarily installed equipment. The J prefix is used for aircraft that can be reasonably returned to their original configuration following tests. An example is aircraft used as testbeds for new electronics, but which will or may not retain that equipment after tests are complete. N Permanent Special Test. Applied to craft involved with special testing on a permanent basis, with modifications to their configuration that make return to original configuration impractical. Many military aircraft transferred to NASA for aeronautical research carry this designation. X Experimental. Applied to craft which are not yet accepted for service, or to prototypes for which standard configuration has not been finalized. Most prototypes of the past carried this prefix, but it should not be confused with craft given an X basic mission symbol. The X status prefix is for designs for other missions, but at an experimental stage of the design process. Y Prototype. Originally applied to demonstration craft where configuration had been determined, but from the 1970s on applied to all prototypes of aircraft intended for production. Z Planning. Applied to designs in the planning/pre-development phase. Rocket/missile launch environment All rockets and missiles contain a symbol to indicate the launch method, be it from the air, ground, sea, etc. The following are the currently authorized symbols for launch environments. These are not used for other aerospace vehicles. A Air-launched. The missile is launched from an airborne vehicle. Example is the AIM-9 Sidewinder dogfighting missile. B Multiple. The missile can be launched from various environments. The BGM-109