Notes for Vehicle Type Symbol:

1. The "B" and "S" type letters were introduced in the 1988/89 time frame, and almost all actual MDS's using these letters were established at the same time. Since then, essentially all new boosters (e.g. the Atlas V and Delta 4) and several satellites have not received an MDS designation. Furthermore, the booster and satellite MDS's are never mentioned outside a few formal DOD documents.
    
2. From 1963 to 1997, reusable UAVs were also covered by the "M" type letter. Since 1997, these vehicles have been designated in a new Q-for-UAV series in the aircraft designation system.
    
3. A "probe" is defined as a non-orbital instrumented vehicle used for meteorological and other measurements (i.e., a sounding rocket). As such, the "N" vehicle type is effectively superfluous, because every probe could be classed within one of the types "M" (if the probe is guided) or "R" (if it is not).
    
4. The "R" vehicle type covers unguided rockets. The original regulation of 1963 explicitly excluded line-of-sight ground-attack rockets from the designation system. Although this is no longer explicitly stated in the current definition, it is still common practice not to assign MDS designations to these types of rockets.
    

Notes for Mission Symbol:

1. It is interesting to note that there is no mission letter for "Experimental". This means that purely experimental vehicles (other than prototypes of operational vehicles) are not intended to receive MDS designations. There is also no designator for "Reconnaissance", although this is definitely a useful purpose for unmanned vehicles. Until the 1990s, reconnaissance UAVs were designated xQM-n (i.e. the same as target drones), while new recce UAVs are designated RQ-n (see also note 4 below). Reconnaissance satellites, on the other hand, do not receive MDS designations, presumably because they are operated by the NRO (National Reconaissance Office) and not the military.
    
2. As of October 2018, the "C" and "M" mission symbols have not yet been used for any MDS designation.
    
3. "I" covers interception within and outside the atmosphere. The designation ASM-135A for an anti-satellite missile project was allocated before the "S" mission symbol had been properly defined. Nowadays, such a missile would be designated as AIM-n.
    
4. The "Q" mission symbol used to be assigned for both target drones and recoverable UAVs. However, in 1997 a Q-for-UAV vehicle type letter was introduced in the aircraft designation system, and since then the letter "Q" in the missile designation system is limited to targets.
    
5. "W" covers vehicles (probes or satellites), which are gathering and/or distributing meteorological data.
    

Notes for Launch Environment Symbol:

1. "B" should only be used, if the missile is essentially unmodified for the different launch options. If several variants of a missile exist for different launch environments, these variants should receive different designations (e.g. air-launched AGM-84A and submarine-launched UGM-84A).
    
2. In this context, a "coffin" is defined as a non-hardened container.
    
3. "G" is primarily meant for runway-launched vehicles. Otherwise, it should only be used if none of the other letters for ground launched vehicles ("C", "F", "H", "L", "M" and "P") can be applied. As a result, "G" is rarely used.
    
4. "H" is used for missiles, which are stored in a silo, but launched from the surface. Such technology was only used for first-generation ICBMs (HGM-16F and HGM-25A), and is now obsolete. Therefore, launch environment symbol "H" is effectively unused today.
    
5. A "soft pad" is defined as a fixed, but unprotected surface location.
    
6. The "S" launch environment symbol has so far only been used in the SSB-n designations for upper stages of space launch vehicles.
    

Notes for Status Prefix Symbol:

1. A "captive" variant of an air-launched missile is one, which can be carried by aircraft (for training purposes) but not actually launched.
    
2. A "dummy" missile is a completely inert round (without motor or warhead), which can be used for ground handling and loading training.
    
3. A "J" prefix is used if the vehicle can be converted back to standard configuration after the tests have ended. The "N" prefix is used for vehicles, which are modified so extensively for special tests, that a reconversion to the original configuration is neither planned nor feasible at reasonable costs.
    
4. The "M" status symbol was apparently considered as unnecessary.
    
5. "Z" is hardly used nowadays. Current aerospace vehicle projects very rarely receive a designation before the actual prototype is under construction, and even if they do the "Z" prefix is often not applied.
    

1. Source [3] (1974 ed.) lists SAM-N-7 as the old designation for Tartar. Since Tartar was a direct development of Terrier, the original SAM-N-7, it is possible, that the Navy at some time started to refer to both systems as SAM-N-7.

2. Several sources list the AQM-35 as the Bendix Talos, with an old designation of XQ-4B. Some of these sources say that there was also an RIM-35 designation, implying a shipborne surface-to-air missile. But the designation of the Talos SAM was of course RIM-8. While it seems to be certain, that Bendix produced a batch of XQ-4B drones originally designed by Radioplane, the XQ-4 is a vehicle completely different from the Bendix SAM-N-6/RIM-8 Talos missile. That said, it can be safely assumed that there was never a "RIM-35" missile, and that the sources saying so are in error.

3. The Nike Zeus A was developed into the Nike Zeus B/Spartan exo-atmospheric interceptor component of the Safeguard ABM system (the endo-atmospheric short-range component was Sprint). Several sources claim that Nike Zeus A was designated XLIM-49A, and Spartan became LIM-49A, although it was significantly different from Nike Zeus A. However, official records clearly indicate that XLIM-49A was actually the Nike Zeus B, which was far more similar to the Spartan.

4. The AN/USD-n designations are from the Joint Electronics Type Designation System (JETDS). The designations apply to the complete drone surveillance system, including ground equipment (the AN/USD series includes - among other equipment - also some drones, which were not redesignated in the missile series). The USD designator means:

• Installation indicator "U": Combination (air and ground in this case)
• Type indicator "S": Combination
• Purpose indicator "D": Surveillance

5. The AGM-62 Walleye is an unpowered glide bomb and shouldn't have been designated in the missile series. The US Navy actually dropped the AGM-62 designator soon after it had been allocated, and designated the Walleye as Guided Weapon Mk 1 instead (later versions received higher Mark numbers). No GBU-n/B designation was used, because the GBU designator did not yet exist in 1963.

6. The missile project number 68 is also reported as AGM-68, but this is incorrect. Also related to the M-68 slot is the U.S. Navy's request in 1995 to assign the designation RIM-68A to the Standard Missile Block IV (as a continuation from RIM-66 and RIM-67). However, the request was turned down, and the missile became the RIM-156A instead.

7. Although it is likely that the designation LEM-70A was reserved (but apparently not used) for the Minuteman ERCS, I have no definite confirmation for this.

8. The XGQM-93A, YGQM-94A, YGQM-98A and XAQM-103A were originally designated XQM-93A, YQM-94A, YQM-98A and XQM-103A, respectively. This was in accordance with the original designation system, which allowed omission of the launch-environment letter when a status prefix was used.

9. The XLIM-99A and XLIM-100A designations were reserved for the US Army in October 1972. This strongly suggests that the numbers were assigned to the silo-launched anti-ballistic missiles then in development. One possibility would be Martin-Marietta LIM-99 Sprint and LIM-100 Sprint II (advanced Sprint, later cancelled), but I have no evidence for this.

10. Some sources say that the RIM-101 is the Sea Sparrow, later designated as RIM-7. Also, the original AIM-101 designation of the Air Force Sparrow is sometimes listed in the "101" slot of the 1963 system. However, both of these descriptions are incorrect. The official source [3] describes the RIM-101A as a "tube-launched SAM, with passive radar and IR guidance", which does not fit the original RIM-7E Sea Sparrow. The most plausible explanation for the confusion is that the RIM-101 was an advanced Sea Sparrow derivative, which was later cancelled in favour of further RIM-7 development.

11. The PQM-102 designation is unusual:

• Usually, drone conversions of manned aircraft are indicated by a Q prefix, i.e. QF-102
• It is a coincidence that the "102" missile number became available just in time for the F-102 drones. Although it might look as if the PQM-102 number was assigned out-of-sequence, this was probably not the case.
• At the time when the drone was designated, the G-for-Runway launch environment letter did not yet exist. Therefore a P-for-Soft Pad letter was used as the best available option.

12. The Navy initially used the BGM-109 designation for all Tomahawks, using numerical suffixes (e.g. BGM-109A-1) to differentiate between the various launch options. This was later appropriately changed to different launch environment letters (RGM-109, UGM-109). The USAF BGM-109G Gryphon GLCM should have been designated MGM-109G, because it was used only from a mobile ground launcher.

13. The FQM-117A is a very simple model plane, while FQM-117B/C are 1/9th scale models of MiG-27 and F-16 aircraft, respectively.

14. It was planned to develop a mobile basing system for the Peacekeeper. The mobile missile would have been designated MGM-118A.

15. ASAT should have been designated AIM-135A, because purpose-indicator letter "I" is defined as "air and space intercept".

16. The ADM-141A/B are unpowered glide decoys, while the ADM-141C ITALD (Improved TALD) is a powered derivative.

17. The designations YPQM-149A and YPQM-150A were reserved for the two finalist contractors (McDonnell Douglas and IAI) for the joint Army/Navy UAV-SR requirement of 1990. However, it was apparently never formally established which design number would refer to which contractor's design. In the end neither designation was ever used before the whole UAV program was restructured.

18. The original AGM-154A/B/C JSOW are unpowered guided glide bombs and should have received GBU-n/B designations. The planned AGM-154D/E variants are turbojet-powered derivatives.

19. The GBSD had the designation LGM-182 originally allocated to it. It is unknown, why this was changed to the out-of-sequence designation LGM-35.

20. The out-of-sequence designation MIM-147A was assigned to an unidentified missile for the USN and/or USMC. It is an unexplained re-use of the 147 slot in the series, and it's not really clear, to which missile it refers. One possible candidate is the Tamir missile of Rafael's Iron Dome system.

21. The designations RQ-1A/B are used by the USAF for the whole Predator system, including ground equipment. The designations RQ-1K and RQ-1L apply to the UAVs of the RQ-1A and RQ-1B systems, respectively. The Predator GCS (Ground Control Station) is called RQ-1P, and the "Trojan SPIRIT II" SATCOM (Satellite Communication) station is designated RQ-1U. The designation MQ-1B refers to the Predator system with UAVs modified to carry the AGM-114 Hellfire anti-armour missile, and the armed UAVs are called MQ-1L. RQ-1Q is an upgraded GCS, and RQ-1W is a new SATCOM station (known as PPSL - Predator Primary Satellite Link). A further upgrade of the GCS is designated as MD-1A, though (in a new "D-for-Drone Control System" series).

22. The Q-12 design number was originally requested by the Army for the YMQ-12A, but rejected in favor of YMQ-1C. The Q-12 slot remained unassigned for several years, until it was filled with the allocation of RQ-12A.

23. It is unclear, why the Q-20 slot was used for the Avenger, when the RQ-20 designation for Puma AE is still in use. However, MQ-20A is not an officially assigned MDS.

24. It is unclear, why the out-of-sequence number 35 was assigned to the V-BAT.

25. XQ-58A and XQ-67A are out-of-sequence designations, where the numbers were taken from the X-series. When XQ-58A and XQ-67A were assigned, the numbers 58 and 67 were the next in line in the X-series. A plain X-58 designation was never assigned, and it's effectively certain, that X-67 will be skipped as well.

26. It is unclear, why the out-of-sequence number 72 was assigned.

27. The number 170 is derived from Lockheed Martin's in-house designation P-170.

1. The RCU-n/B designations were defined in the Aeronautical and Support Equipment Type Designation System (ASETDS), which includes air-dropped ordnance. The "RCU" designator has been deleted from the ASETDS since at least 1974, and I have no references as to its exact meaning. Most likely, it was either "Rocket, Chaff" or "Rocket, Decoy".

2. AGR-19, AGR-20 and AGR-21 are incorrectly designated as unguided rockets. They are guided missiles, and as such should have been designated AGM-n.

1. The S-10 slot in the satellite series was reused for unknown reasons. The "XSS" prefix of the MDS designation has since been used as an acronym with various interpretations ("Experimental Small Satellite", "Experimental Spacecraft System", "Experimental Satellite System").

2. Other than XSS-10A, the designations of the XSS-11 and XSS-12 follow-on programs were not official MDS designators. However, because of the relatively wide-spread use of the XSS-11 and -12 labels at the time, the numbers S-11 and -12 have not been assigned to other satellite programs to avoid confusion.

3. The design number 13 has been skipped, because that number is not used anymore in any MDS designations (triskaidekaphobia).

4. The designation LS-15A almost certainly refers to the SBSS (Space-Based Space Surveillance) satellite, but this is not confirmed with 100% certainty.