communications personnel to handle it properly. It contains all the components shown in figure 3-3. STATION AND ADDRESS DESIGNATORS LEARNING OBJECTIVES: Define station and address designators; explain procedures for constructing call signs and address groups. List procedures for establishing and maintaining communications. Station and address designators are any combinations of characters or pronounceable words designed for use in message headings to identify a command, authority, unit, or communications facility, or to assist in the transmission and delivery of messages. Station and address designators encompass four categories: call signs, address groups, plain language, and routing indicators. CALL SIGNS Call signs are letters, letter-number combinations, or one or more pronounceable words used for establishing and maintaining communications. Call signs may also be used as address designators when the call sign indicates the addressee or originator. The following list contains the different types of call signs: 1. International 2. Indefinite 3. Net 4. Tactical 5. Voice 6. Visual 7. Signal letters of ships and signal letters identification numbers of aircraft when used international call signs International Call Signs or as International call signs are assigned to radio stations in all countries—civil and military, afloat and ashore—according to international agreement. The first letter or first two letters of a call indicate the nationality of the station. The United States has the first half of the A block (through ALZ) and all of the K, W, and N blocks. The United States reserves A calls for the Army and Air Force. The K and W blocks are assigned to commercial and private stations, merchant ships, and others. The N block is for use by the Navy, Marine Corps, and Coast Guard. Naval shore communication stations have three-letter N calls. If necessary, these calls may be expanded by adding numerical suffixes. Thus, additional call signs are provided for facilities located remotely from the parent station. Examples are the following: NAM. . . . .NAVCOMMSTA, Norfolk NAM1 . . . . Headquarters, CINCLANTFLT, Norfolk NAM2 . . . . Naval Shipyard, Norfolk International call signs assigned to U.S. naval ships are four-letter N calls, which are used unencrypted only. They have no security value; hence they are authorized for use with Allied, civil, and merchant stations. An example follows: NJUL. . . . .USS BAINBRIDGE (CG(N) 25) International call signs for USN, USMC, and USCG aircraft are composed of the service designator N, NM, or NC, respectively, followed by the last four digits of the serial number of the aircraft. Indefinite Call Signs Indefinite call signs represent no specific facility, command, authority, or unit, but may represent any one or any group of these. Examples: NERK NAthrough NZ . . . . . (From) any U.S. Navy ship Indefinite call signs are used in codress message headings to conceal the identity of originators and addressees. In such instances, the address component is placed in the encrypted text. Net Call Signs Net call signs represent all stations within a net. (A net is a group of stations in direct communication with each other on a common channel.) Normally, net call signs are not used in visual transmissions. Following is an example of a net call sign: NQN. . . . All U.S. Navy radio stations in the Pacific guarding the ship-shore high-frequency calling series 3-11