Merchant Navy Convoys – BAMA protocol

From Wikipedia:

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 merchantmen in any part of the world. The BAMS system is designed for communication by the best employment of radio stations available.

BAMS Zones of Operation across the world 1944.

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 listed 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In 1942, the GBMS system was superseded by the combined Anglo-American system of BAMS, and the addition of US Navy W/T stations improved the poor coverage.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.

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 Zones.

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 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.