...what is now known as the "International Code of Signals" has since been adopted by the following nations for use of national as well as merchant ships: England, France, Germany, Russia, Brazil, Italy, Austria, Holland, Spain, Sweden and Norway, Denmark, Belgium, Portugal. Although in general use by vessels of the United States as well as other countries, our Government has not yet formally recognized the "International Code".Under the provisions of the International Code of Signals, 1,440 four-letter combinations from GQBC through GWVT were reserved as ship identifiers for men-of-war and government vessels, while merchant ships drew upon 53,040 combinations from HBCD though WVTS. (Ship identifiers were always four different letters, i.e. no letter appeared more than once. Also, until 1901, there were only 18 letters, all consonants, in the International Code.) Displaying a ship's visual identifier required six flags -- the National Ensign, the Code Pennant, plus a letter flag for each character in the ship's four-letter identification. Because more than one country could assign the same four-letter identifier to a ship, the National Ensign was used to differentiate between vessels from different countries.
The service regulations of the Berlin Radiotelegraphic Convention provide that every wireless ship or shore station shall have its own call letters (signifying its name), which must consist of three letters of the alphabet. [NOTE: Although U.S. representatives had signed this convention in 1906, the U.S. would not formally ratify it until April 3, 1912.] To prevent duplication of call letters is one of the duties of the International Bureau of Telegraphs at Berne, Switzerland, which has charge of general administrative work in the interest of wireless telegraphy. Call letters for American ships equipped with wireless have been assigned almost haphazard by the wireless companies. The Code List for 1911 (pp. 102-103) contains a list of 361 American merchant vessels and yachts, arranged according to their wireless call letters. This publication was for the convenience of shipmasters in signaling, but the list when assembled shows defects. In some instances three letters of the alphabet are used, in others a letter and a number, and in others a number alone. Where two letters are used, in 6 cases the same two letters have been assigned to three vessels, and in 25 cases the same letters have been assigned to two vessels. It is time that the United States brought its wireless code into conformity with that of the rest of the world, just as our code of signals by flags and pennants is the international code. There must be a central bureau to assign wireless call letters to merchant vessels and yachts to prevent duplications and to bring these call letters into accord with the system adopted by the rest of the maritime world. Under the three-letter call adopted by the Berlin convention, over 18,000 distinctive calls can be assigned without duplication. This number will suffice for the wireless ship and shore stations of the world for years to come. The two-letter system now employed by the wireless companies in the United States will soon exhaust itself. The Bureau of Navigation was charged by the act of July 5, 1884, with the assigning of signal letters to American merchant vessels, and is making arrangements to assign wireless call letters at the same time, and do for the wireless code the work it now performs for the international code.The authority to assign radio call letters to ships, which Chamberlain claimed under the July 5, 1884 act, did not include land stations. (At this time the U.S. government had not yet started licencing radio transmitters). The date of the changeover to the new three-letter radio calls wasn't stated in the 1911 annual report, however, an October 25, 1912 General Letter from the Department of Commerce and Labor later referred to "the call letters assigned to American ship stations on July 1, 1912, by the Bureau of Navigation". (U.S. merchant ships were still using their old two-letter calls according to the January 1, 1912 edition of the Navy's Wireless Telegraph Stations of the World, but the new three-letter calls are listed in the radio call letter list in the June 30, 1912 edition of the Annual List of the Merchant Vessels of the United States, with K calls assigned to ships on the "Atlantic and Gulf Coasts", and W calls going to the "Pacific Coast" vessels.) In many cases, all that was done was to add a K or W in front of the ship's original two-letter call -- see 1911-1913 Ship Callsign Comparison Chart for more details. I don't know why K and W were chosen for the initial letters, or why the Bureau thought it necessary to split the assignments into two geographic groups -- they had not done anything similar with the visual signal letters. It is possible that W stood for "west", but that is pure speculation on my part.
The London International Radiotelegraphic Conference made a partial allotment of call letters among nations which signed the convention and the International Bureau at Berne, with the consent of such nations, has modified and added to this assignment of call letters by circular of April 23, 1913. The distribution of call letters among nations thus authorized is printed below for the guidance of operators of all stations, ship and shore, of the United States.
A.............All to Germany and protectorates. B.............All to Great Britain. CAA to CMZ....Not yet assigned. CNA to CNZ....Morocco. COA to CPZ....Chile. CQA to CQZ....Monaco. CRA to CTZ....Portugal and colonies. CUA to CUZ....Not yet assigned. CVA to CVZ....Roumania. CWA to CWZ....Uruguay. CXA to CZZ....Not yet assigned. D.............All to Germany and protectorates. EAA to EGZ....Spain and colonies. EHA to EZZ....Not yet assigned. F.............All to France and colonies. G.............All to Great Britain. HAA to HFZ....Austria-Hungary and Bosnia-Herzegovina. HGA to HHZ....Siam. HIA to HZZ....Not yet assigned. I.............All to Italy and colonies. J.............All to Japan and possessions. KAA to KCZ....Germany and protectorates. KDA to KZZ....United States. LAA to LHZ....Norway. LIA to LRZ....Argentine Republic. LSA to LWZ....Not yet assigned. LXA to LZZ....Bulgaria. M.............All to Great Britain. N.............All to the United States. OAA to OFZ....Not yet assigned. OGA to OMZ....Austria-Hungary and Bosnia-Herzegovina. ONA to OTZ....Belgium and colonies. OUA to OZZ....Denmark. PAA to PIZ....Netherlands. PJA to PJM....Curacao (Dutch). PJN to PJZ....Surinam (Dutch). PKA to PMZ....Dutch East Indies. PNA to PZZ....Not yet assigned. Q.............Reserved for code abbreviations. R.............All to Russia. SAA to SMZ....Sweden. SNA to STZ....Brazil. SUA to SUZ....Egypt. SVA to SZZ....Greece. TAA to TMZ....Turkey. TNA to TZZ....Not yet assigned. UAA to UMZ....France and colonies. UNA to UZZ....Austria-Hungary and Bosnia-Herzegovina. VAA to VGZ....Canada (British). VHA to VKZ....Australian Federation (British). VLA to VMZ....New Zealand (British). VNA to VNZ....South African Union (British). VOA to VOZ....Newfoundland (British). VPA to VSZ....British colonies not autonomous. VTA to VWZ....British India. VXA to VZZ....Not yet assigned. W.............All to the United States. XAA to XCZ....Mexico. XDA to XZZ....Not yet assigned. YAA to YZZ....Not yet assigned. ZAA to ZZZ....Not yet assigned.
The call letters assigned to the United States are all combinations (676) beginning with the letter N and all (676) beginning with the letter W, and all combinations (598) from KDA to KZZ, inclusive. [NOTE: KAA-KCZ was allocated to Germany at this time, and was not assigned to the United States until 1929.] The total number of international calls is thus 1,950, and these are reserved for Government stations and stations open to public and limited commercial service. All combinations beginning with the letter N are reserved for Government stations and in addition the combinations from WUA to WVZ and WXA to WZZ are reserved for the stations of the Army of the United States.
The combinations KDA to KZZ, with a few exceptions, are reserved for ship stations on the Atlantic and the Gulf of Mexico and for land stations on the Pacific coast. The combinations beginning with W (except WUA to WVZ and WXA to WZZ as already indicated) are reserved, with a few exceptions, for ship stations on the Pacific and Great Lakes and for land stations on the Atlantic and Gulf coasts and in the Great Lakes region.