Page 635 radio acoustic ranging 674 



674. Communication System 



To coordinate the operations at the various stations on a vessel using R.A.R., an 

 adequate communication system is essential. This system includes interconnected 

 electric bells, located near the chronograph attendant and on the bridge. The bomber, 

 at his station near the stern of the vessel, may ring these simultaneously by means of 

 a portable push button which he can carry in his hand while tlirowing the bomb over- 

 board. Another bell is located at the bombing station, connected to be rung either by 

 the chronograph attendant or from the bridge, depending on who orders the bombs. 



If the chronograph station is remote from the plotting station and if the latter is 

 not located on the bridge, a communication system must be provided between the three, 

 so that data and orders may be rapidly and accurately transmitted. The R.A.R, time 

 intervals for each position must be transmitted from the chronograph station to the 

 plotting station with a minimum of delay and, where the plotting is not done on the 

 bridge, orders relative to the navigation must be transmitted from the ofl5cer-in-charge 

 to the watch officer on the bridge. Speaking tubes or telephones may be used for this 

 purpose, but instruments used for interoffice communication are much more satisfactory. 

 The latter are made under various trade names by a number of manufacturers of 

 electric equipment, but any selected should be adapted for use on shipboard. A loud- 

 speaker type of unit is desirable, arranged so that a lever is pressed to talk and released 

 to listen. This leaves both hands free for copying any transmitted data. 



6741. Bombing Station Signals 



In Radio Acoustic Ranging (R.A.R.) bombs of various sizes are required, depending 

 on the distances from the R.A.R. stations and other factors which inffiience the trans- 

 mission of sound. The chronograph attendant is able to judge the size of bomb 

 required by observing the character of the radio returns from the stations. The same 

 size of bomb will often be used continuously for a considerable period of time, but it is 

 occasionally necessary to change; and a system of bell signals should be provided to 

 notify the bomber of the size of bomb wanted at each position, and when to light the 

 bomb and throw it overboard. 



The signals are given by the chronograph attendant, or from the bridge, by ringing 

 a bell at the bombing station. The signals for bombs of different sizes may be various 

 combinations of long and short rings, a long ring being approximately three times the 

 duration of a short ring. The following signals are recommended: 



Type of bomb Signal 



Single detonator Five short rings. 



One-quarter pint One long ring. 



One-half pint Two long rings. 



One pint Three long rings. 



One quart One long and one short ring. 



For bombs of other sizes, suitable signals may be arranged. 



The clock at the chronograph station should be synchronized with the clock used 

 for sounding. At 1 minute before a position the bomber is given the signal designating 

 the size of bomb desired. The bomber answers this signal immediately with two long 

 rings, indicating that the signal has been received and understood; this acknowledg- 

 ing signal is received both by the chronograph attendant and on the bridge where it 

 serves as a stand-by signal for any observations to be taken on the position. Ten or 

 15 seconds before the position the bomber is notified to light the bomb, by one extra- 



