Broadcast to Allied Merchant Ships
Broadcast to Allied Merchant Ships (BAMS) was a protocol and system of broadcasts for Allied Merchant ship convoys that was used during World War II to provide for the transmission of official messages to merchant ships in any part of the world. The BAMS system is designed for communication by the best employment of radio stations available. Background. On the outbreak of World War II, the British Admiralty took over control from the GPO, and the embryo merchant ship broadcast system, called "GBMS" came into force. Ships listened at routine times to the Rugby Radio  Station and to area stations, otherwise keeping watch on the international distress frequency at 500 kHz. After the fall of France, the Admiralty assumed control of all Allied merchant shipping which complied with British procedures. When America entered the war, the world was divided into two strategic zones, the Admiralty being responsible for merchant shipping in one, and the United States Navy in the other. The GBMS organisation proved to be inadequate for the efficient clearance of traffic for a number of reasons, including poor coverage by Wireless telegraphy (W/T) stations, obsolescent equipment, and many ships only able to  listen at single or two operator periods. The systems gradually improved, and from 1942 all Allied merchant ships had to have two radio technicians on board, with more modern equipment being fitted to ships. In 1942, the GBMS system was superseded by the combined Anglo-American system of BAMS, and the addition of US Navy W/T stations improved the poor coverage. For ship to shore communications, during Radio silence, ships in Convoy passed any essential messages through their escort for transmission. The Commodore's and Vice-Commodore's ships, rescue ships, merchant aircraft carriers, and ships fitted with Huff  Duff were fitted when possible for intercommunication with other escort vessels. In 1943 Rodger Winn persuaded the Admiralty that German code breaking in World War II was reading BAMS messages, requiring a change in cipher methods. Description. The BAMS protocol was the second part of a two part communication protocol between shore to merchant ship. BAMS was for Radio communication, and the Visual signalling component, the first part was, called the: Visual Signalling Code and Instructions (WIMS-I), a publication held by the United Nations. Both BAMS and WIMS-I were essentially a safety protocol, to ensure reliable, "no mistake  communication. Shore to Ship Communication. The BAMS system divides the world into three zones, that are covered by a high-powered Zone station. Each zone is further sectioned with an Area station per section. Within a zone, multiple stations synchronize using Spread spectrum frequency radio to provide complete coverage. Image one called: BAMS Zones of Operation" has a clear description, of delineation of control with the Zones. BAMS Delineated Zones. The following is an example of Area 1B. The Area 1B record provides an English description of a topographic square on the earth. Area 1B record is record 2 of  20, and has the following format: The Zones are numbered, Area 1A, Area 1B, 2A, 2B, 3A, 3B, 3C, 4, 5A, 5B, 5C, 5D, 6A, 6B, 6C, 7A, 7B, 7C, 8 and 9. Operation. Zone and Area stations were configured to broadcast at routine times, on intermediate and high frequencies, with general or individual ship addressed messages, in their own zone of area, respectively. Coastal stations were utilized for the broadcast of messages to merchant ships within range, except at times when broadcast schedules within that zone are in operation. Coastal stations called on the 500 kHz frequency band, and  shifted to the working frequency, for the transmission of the BAMS message. Arranging Authority. Transmissions of messages for merchant ships via the Zone, Area or Coastal stations are arranged by certain designated shore-based "Arranging Authorities" (AA). These stations read the BAMS "message header" and route the BAMS messages, ensuring it is transmitted by correct Zone and Area stations assigned to them, and by Coastal stations if required. The Arranging Authority also ensures that Coastal stations under their control, transmit messages that are considered necessary, even if the originator does not specify such a transmission. Originators responsibility. The originator of  a BAMS message is responsible for routing the message to the AA, controlling the Zone and Area stations. In addition, the originator of the BAMS message is responsible for routing to concerned authorities. Routed BAMS messages are only sent to those radio stations whose plotted position covers the area addressed in the BAMS message. An AA may need to know the content of the BAMS dispatch but doesn't require forward routing via the station under its control. In this instance, the message is addressed using the format described in Addressing, described below. In the case of general messages, the  Zone and Area station at least would always be utilized and the case of individually addressed messages, the Area station and appropriate Coastal stations would always be utilized. Routing. When ships are passing from one area to another, messages which concern them all are routed via the Area stations of both areas and via the appropriate Zone station. BAMS Procedures. Operating Signals. In order to facilitate the handling of BAMS messages, Combined Operating Signals for worldwide use had been allocated as follows: These procedures signals were used in connection with unenciphered US Navy call signs or combined call signs as  appropriate. All transmissions of BAMS messages between naval authorities must carry appropriate procedures signals except where messages are transmitted to radio stations for broadcast where no intermediate relaying station is involved. BAMS Headings. A modified commercial procedure is utilized for the addressing of BAMS messages and immediately follows the procedure signals, radio station call signs and station serial number. Component parts of this BAMS heading would always appear in the following order: BAMS Instructional Group. The Instructional Group consists of two elements, the first and second letters should be considered together as should the third, fourth and fifth letters, as  show in the following table: The following is an example: Group XY having been assigned, the call sign used to address the whole convoy is XYD3. The following is an example: Addressing BAMS traffic. The following lists several examples of BAMS traffic addressing. Correction of BAMS messages. Occasionally a BAMS message needed to be corrected. In this instance, a new enciphered message was created, and dispatched using the same instruction group. Corrections to errors in transmission of code groups took the form of a new plain language dispatch containing appropriate instructions regarding the changes.