which provide navigational assistance. Q Drone. Applies to a vehicle designed to be remotely controlled. Ballistic/semi-ballistic vehicles, cruise missiles, and artillery projectiles are not considered drones. S Space support. Applies to vehicles designed to support space programs and activities. T Training. Applies to aircraft used in training. U Underwater Attack. Applies to vehicles designed to attack submarines and underwater targets. W Weather. Applies to vehicles designed to obtain weather data and collect aerial samples. Vehicle type symbol For rockets and missiles, the vehicle type symbol identifies the basic vehicle type and will be the final symbol in the mission part of the MDS. B Booster. Boosters are primary or auxiliary propulsion units for other vehicles. M Guided Missile. Guided missiles are unmanned vehicles flying a path controlled by a guidance system. N Probe. Probes are non-orbital unmanned vehicles designed primarily to collect data within the aerospace environment. R Rocket. Rockets are single-use unmanned vehicles without guidance after launch. S Satellite. Satellites are space vehicles which orbit the earth and used to collect and transmit various data. Design number The design number is separated from the earlier components by a dash. Design numbers run consecutively from 1 to 999. Series The series letter follows the design number and progresses consecutively starting with A. In the event the series letter "Z" is used, the design number will progress to the next unused number and series will begin again at "A". To avoid confusion, series "I" and "O" are not used. Additional Components Configuration/Component number Configuration/component numbers signify changes that "affect performance, tactics, or integral components of a weapon system." They appear to the right of the series symbol and are separated from the series symbol by a dash. Block number The block number specifies a group of aircraft produced to the same specifications by the manufacturer. Block numbers are assigned in multiples of 5 (01, 05, 10). Serial number Serial numbers are located on the tail and identify a specific rocket/missile. For more information on serial numbering of military aircraft, see United States military aircraft serial numbers. Exceptions The F-117 Nighthawk does not currently have any air-to-air capabilities which raised the question of why it was designated F-117 and not A-117. There has been conjecture and anecdotal reports concerning purported air-to-air capabilities targeted toward destroying Soviet AWACS craft. Although the mission letters of the AV-8 Harrier's designation are correct, the series number