6843 HYDROGRAPHIC MANUAL PaGE 648 



As soon as the signal for a bomb has been received, the bomber takes a bomb of the 

 size ordered and places it on the workbench. A slender nonmetallic tool is inserted 

 through the hole in the top of the can, to make a cavity in the TNT with a diameter 

 equal to that of the detonator. The detonator is inserted well within the container so 

 that it is embedded in the TNT. With a blunt nonmetallic tool the burs around the 

 hole in the top of the can are pressed around the fuse, taking care not to puncture the 

 fuse with the sharp edges of the burs. The can does not have to be watertight, but 

 the crimp between the fuse and detonator does have to be watertight. 



The final preparation of cast-iron bombs, or bombs in the other types of containers, 

 is similar to the above. The fuse for cast-iron bombs should be inserted in the hole in 

 the stopper. A cavity for the detonator is made in the TNT and the stopper with 

 detonator attached is firmly pressed into place. 



6843. Fuse Length 



A fuse used in detonating an R.A.R. bomb must be sufficiently long to allow the 

 ship to pass out of danger before the explosion occurs, but should not be so long that 

 the bomb will sink to a depth where a misfire is likely. Furthermore, it is desirable to 

 keep the fuse interval as short as practicable, consistent with safety, for the sake of 

 accuracy (see 6853(6?)). 



Varying lengths of fuse are generally required for bombs of different sizes, for best 

 results seem to be obtained when the bombs explode at about the same depth as the 

 hydrophone of the receiving unit, which is approximately 7 fathoms for sono-radio 

 buoys. To accomplish this, the rate of sinking of different types of bombs should be 

 determined by experiment (see 6846) and a sufficient length of fuse should be used 

 to explode each type of bomb at the desired depth. 



a. Fuse interval. — The fuse interval is the interval between the time the bomb is 

 thrown overboard and the time it explodes. It is necessary to know this interval to 

 the nearest second in order to compute the ship's run correction (see 6853(c?)). For 

 this purpose the time of the bomb explosion can be assumed coincident with its receipt 

 on the chronograph. The fuse interval is timed by means of a stop watch or from 

 the second hand of a clock, except with the Dorsey chronograph where it is recorded 

 on the tape (see 6813). The chronogi-aph attendant records the interval in the Bomb 

 Record. 



6844. Igniting Bombs 



With the prepared bomb in hand, the bomber stands by the electric heating ele- 

 ment ready to light the bomb. The outer covering at the end of the fuse which is to 

 be ignited should be pressed back slightly to expose the powder train. At the signal 

 to light the bomb, the fuse is held against the electric heater until ignited. This is 

 evidenced by a tongue of flame and spitting sparks about 2 inches long that shoot out 

 of the end the instant the fuse is lighted. This continues for about a second and is 

 followed by smoke rising from the end of the fuse. The presence of smoke indicates 

 that the fuse is burning internally. 



Other methods of lighting fuses may be used which dispense with the electric heat- 

 ing element. Two accessories are manufactured for this purpose. One is known as a 

 "pull wire fuse lighter," designed for use during rainy weather; it fits over the end of 

 the fuse and lights the fuse when a wire is pulled. The other, known as a "safety fuse 

 match lighter," seems better adapted for use in R.A.R. It is a short paper tube that 

 can be slipped over the end of the fuse. One end of the tube is coated with the igniting 



