663 HYDROGRAPHIC MANUAL PaGE 620 



For the best transmission of sound, the bombs should not explode too close to the 

 surface of the water. An additional weight must be placed in tin can bombs to make 

 them sink deeper before they explode. Pieces of scrap metal have been used for this 

 purpose and dry sand and concrete have also been used. The quantity of sand required 

 to make the bombs sink to a sufficient depth reduces the explosive capacity, but this 

 results in very little apparent difference in the effective range. Melted pig lead is 

 usually used to weight the tin containers, however, the quantity required varying with 

 the size of the container. About 13.5 ounces of lead is required to weight a 1-pint 

 bomb, and a proportional weight for other sizes. This proportion of lead is sufficient 

 to make the various sizes of bombs sink at a rate of about K fathom per second. (See 

 6846.) 



A hole, slightly larger in diameter than the detonator, is punched with around metal 

 tool in each tin can top. This hole is punched from the inside of the top so that the 

 burs left around the hole will be on top when the lid is in place. The detonator, with 

 fuse attached, is inserted into the TNT through this hole. The fuse protrudes through 

 the hole, the burs being pressed around it to hold it in place and to seal the can 

 somewhat. 



663. Construction of Bombs 



Bombs are generally constructed in two or three separate operations; they are 

 prepared for use in a preliminary operation but are finally completed only just before 

 being ignited and thrown overboard (see 6842) . If the bombs are weighted with sand 

 or scrap metal there is only one preliminary operation, for the container may be filled 

 with TNT immediately after the weights are placed in the cans — ^but if they are weighted 

 with melted pig lead, the lead must be allowed to cool before the TNT is added. 



Where melted pig lead is used for weighting, the tin cans should be prepared while 

 in port to avoid the possible fire hazard on board ship, and in such case as many cans 

 of various sizes should be weighted as will probably be needed during the next month, 

 assuming there is sufficient stowage space. However, if there is a suitable fireproof area 

 in the fiddley, or elsewhere, the cans may be weighted on board. The pig lead, after 

 being cut into pieces that will go in the melting pot, is melted over a suitable forge or 

 large gasoline blowtorch. The cans are set in a shallow tray containing about one-half 

 inch of water and the melted lead is poured into each as required to furnish the nec- 

 essary weight. An experienced man will be able to estimate the required amount 

 within satisfactory limits. 



After the cans have cooled to atmospheric temperature they may be filled with 

 TNT. Only a sufficient number to fill the bomb locker (see 6841) should be prepared 

 at one time. Most port regulations forbid the handling of any type of high explosive 

 in the harbor, so the containers must be filled while at sea. This should be done during 

 good weather in a protected spark-free space on deck, on the lee side if possible, and the 

 space should be surrounded on three sides with a canvas windbreak to prevent the 

 scattering of loose grains of TNT. The deck should be covered with heavy canvas so 

 that it will not be impregnated with TNT (see 666). 



The cans are usually filled from an open box of TNT by a man wearing a special 

 pair of long heavy rubber gloves to protect his hands and arms. A dust mask is also 

 advisable, for TNT is injurious to the respiratory system if inhaled. (See 666.) Each 

 can is filled gradually, the TNT being compacted firmly into the can in the process. 

 To be certain of detonation the TNT must be firmly packed in the container. A 

 wooden implement, similar to a potato masher, with a flat bottom and a diameter 



