6848 HYDROGRAPHIC MANUAL PaGE 650 



If the distances involved are short and only detonators or very small bombs are 

 required, they may be thrown overboard at the buoy from the ship lying-to near the 

 buoy. In such case bombs are ignited and thrown overboard by the bomber at the 

 regular signal from the chronograph attendant, who has the desired number fired in 

 rapid succession, one after the other, without scaling the chronograph tapes until later. 

 The bomber throws the bombs so that they hit the water within a few feet of the buoy, 

 taking care not to hit the buoy structure and damage the bomb. 



Where larger bombs are required, the ship must be underway. The ship follows a 

 figure-of-eight course, passing and repassing the buoy, and a bomb is exploded near the 

 buoy each time the bombing station comes abeam of it. The bomber must watch the 

 buoy as the ship approaches it and judge the distance so as to light the bomb just enough 

 in advance so that it will be ready to throw overboard when the buoy structure is 

 abeam. The ship should be maneuvered so that the bombing station will be within 

 approximately 50 feet of the buoy, when abeam. If the bomber judges that the buoy 

 win be beyond a reasonable throwing distance, when it is abeam, he should not light the 

 bomb at aU. 



6848. Failure to Detonate 



Bombs seldom fail to detonate if they are properly prepared and handled. Any 

 of the following things may occasionally cause misfires: 



(a) Breaking the fuse in handling it or using fuse that has been crushed or walked on. 



(b) Wet fuse ends. 



(c) Cutting the fuse with a dull instrument or cutting it on a slant. 



(d) Fuse fitted improperly, as when the fuse is not seated closely against the explosive in the 

 detonator, or when the detonator is not properly crimped around the fuse. 



(e) Loss of powder from the fuse end before it is inserted into the detonator. 

 (/) Too long a fuse, the bomb sinking too deep. 



ig) Use of too light a detonator. 



(h) Fuse and detonator dislodged from bomb container. 



(z) Throwing bomb overboard before the fuse is burning properly. 



685. Chronograph Tapes 



The chronograph tape is the original record from which the time intervals to the 

 several R.A.R. stations are determined for recording in the Bomb Record. As the 

 chronograph tape is drawn through the chronograph it passes under two styluses that, 

 correctly adjusted, draw coincident lines near the middle of the tape. (See 673.) The 

 timing stylus, when actuated, makes short offsets below the Une at regular intervals, 

 and the signal stylus, when actuated by a bomb or radio signal, makes a longer offset 

 above the line. From these offset marks on the chronograph tape, the time intervals to 

 each station may be determined. 



6851. Reception of Bomb Returns 



After a bomb has been thrown into the water and the chronograph has been started, 

 the chronograph attendant, seated at the chronograph where the tape emerges, holds 

 the hydro-radio switch in the position to receive the bomb signal through the hydro- 

 phone in the hull of the ship. When the offset caused by the bomb explosion is made 

 on a Gaertner chronograph tape, it is marked by pencil for identification — on a Dorsey 

 chronograph tape it is identified by the zero printed with the next tenth second offset. 

 The switch is then released, or otherwise placed in the position, to receive the radio 

 signals fVom the R.A.R. stations. 



