6813 HYDROGRAPHIC MANUAL PaGE 038 



Ten to 15 seconds before 14:18, the bomber is notified by one long bell signal to 

 light the fuse, preparatory to throwing the bomb into the water. 



As soon as the bomber judges that the fuse is burning internally (see 6844 and 

 6845), and not later, the bomb is thrown overboard and as it strikes the water the 

 bomber signals with one long bell. This signal is received at the chronograph station 

 and on the bridge. The time of the signal is recorded as the official time of the position. 

 A soimding is taken, the log is read, and any other observations are made at this tim.e; 

 changes in com'se or speed are also made; and all are recorded in the Sounding Record. 



When the "bomb over" signal is received at the clu-onograph station, the chrono- 

 graph is started and the hydro-radio switch (6724) is held in position so that the bomb 

 explosion will be registered on the chronograph tape. The time in seconds between the 

 ''bomb over" signal and the explosion is determined by a stop watch, from the second 

 hand of a clock, or from the tape of a Dorsey chronograph (see 6733a). This tinie 

 interval is recorded in the Bomb Record (see 6843a). The record of the explosion on 

 the tape of a Gaertner chronograph is identified by a pencil mark near it. 



Immediately after the explosion has been registered on the chronograph tape, the 

 hydro-radio switch is released so that it is in position to allow recording of radio signals. 

 The clu'onograph continues to run until the radio signals from all of the R.A.R. stations 

 have been received and recorded on the tape. As each return is received and heard 

 in a loud speaker, it is also identified on the tape by a pencil mark nearby. After the 

 last radio signal has been received, the chronograph is stopped and the tape with the 

 record is torn off. 



The various time intervals required for determining the elapsed time to each 

 station, for use in plotting, are then taken from the tape or computed, in accordance 

 with 6853, and entered m the Bomb Record. 



As soon as the elapsed times have been accurately determined they should be 

 transmitted to the officer-in-charge at the plotting station. Let us suppose that the 

 number of the position is 89 and that returns were received from three R.A.R. stations, 

 designated as ESAU, DAGO, and GOBY, and that the elapsed times to them, as identi- 

 fied by the chronograph attendant, are 8.56, 19.35, and 27.97 seconds respectively. 

 The data should be transmitted approximately in the following manner: 



The CHRONOGRAPH ATTENDANT calls the plotting station and after an acknowledg- 

 ment, or over the loud-speaker system, says: "Bomb at fourteen eighteen." 



The OFFICER-IN-CHARGE replies: "Position eighty -nine at fourteen eighteen." 

 This enables the chronograph attendant to record the correct position number in the 

 Bomb Record and on tlie chj'onogi-aph tape. 



Chronograph attendant: "Position eighty-nine; ESAU eight fifty-six, DAGO 

 nineteen thirty-five, GOBY twenty-seven ninety-seven." 



The officer-in-charge repeats the elapsed times to the chronograph attendant 

 for verification. 



The elapsed times to the various R.A.R. stations should be transmitted to the 

 plotting station in the order of their length, the shortest being transmitted first. This 

 is the natural order of scaling or reading the radio returns from the chronogi'aph tape, 

 and a little time is saved in making the settings of the fixtures on the beam compass. 



After the elapsed times have been received at the plotting station, they are plotted 

 graphically on the boat sheet using the most probable velocity of sound, and the position 

 is determined. 



Occasionally, at the clu-onogi-aph station, a radio return from an R.A.R. station 

 may be improperly identified, a false mark may be mistaken for a radio return, or an 



