The Detonator Head 



Although it explodes a 

 giant shell it is harm- 



GRAZE PELLET 



PERCUSSION PELLET 

 PERCUSSION SPRING 



THOSE great shell cra- 

 ters which form such 

 commodious quarters 

 for the Tommies to stretch 

 in after weeks of confinement 

 in narrow trenches or which 

 may be improvised into forts 

 on occasion, are mostly 

 formed by the explo- 

 sion of high-explosive 

 shells fitted with de- 

 tonator heads, al- 

 though similar craters 

 may also be formed 

 by detonated shrap- 

 nel. The shattering 

 of fortifications, the 

 demolition of supply depots and most of 

 the damage caused by explosive shells is 

 made possible through the agency of the 

 small detonator fuse or head fitted to the 

 nose of each projectile. 



This little device is simple in construc- 

 tion and is of interest in that two distinctly 

 different forces are required before it will 

 become effective — a centrifugal force for 

 unlocking the mechanism and a detonating 

 force for the explosion. 



On being fired from the gun, the projectile 

 travels at a high rotary speed and the 

 dedent spring is compressed, so that the 

 dedents, acting as virtually one piece, drop 

 down into the dedent spring cavity. The 

 twirling of the shell throws the upper de- 

 dent out of plumb as soon as it drops into 

 the spring cavity. On the recoil of the 

 spring the dedents lock into the larger hole. 

 The twirling of the shell, due to the rifling 

 of the gun, also causes the centrifugal bolt 

 to fly away from the graze pellet once 

 the upper dedent has dropped into the 

 lower cavity, so that the graze pellet is 

 held in position simply by the coiled spring 

 between it and the cap. In the top of the 

 graze pellet is fitted a detonator charged 

 with a highly explosive material. On the 

 arrest of the flight of the projectile, through 



less until it leaves the 

 muzzle of a gun 



PERCUSSION NEEDLE 

 PERCUSSION DETONATOR 



The body of the detonator head carries within 

 it a cylindrical block of material known as a 

 graze pellet, while the cap of the head carries 

 the percussion needle. An alternate detonating 

 device is also provided in the body — one which 

 becomes effective only after the graze pellet 

 has been released by contact. This second 

 detonating mechanism is provided simply to 

 assure explosion and is probably seldom essential 



contact with a solid body, 

 the graze pellet with its de- 

 tonator is thrown violently 

 against the needle in the 

 cap and exploded. The re- 

 sulting flash passes through 

 a central hole in the graze 

 pellet and ignites the powder 

 in the gaine tube and 

 is transmitted through 

 it to the explosive 

 charge at the base of 

 the shell. 



Protruding from 

 the lower end of the 

 graze pellet is a teat 

 which fits into a hole 

 in a kind of transverse carriage known as 

 the percussion pellet. This pellet carries at 

 one end a holder containing at its center 

 the percussion needle around which are a 

 number of flash holes giving direct com- 

 munication through the percussion pellet 

 to the top of the gaine tube. Opposite the 

 percussion needles carried in the body of 

 the head is a second charged detonator. 

 Behind the percussion pellet, or, rather, 

 within the hole bored in its opposite end, 

 is a spring, held in compression by the teat 

 of the graze pellet. When the graze pellet 

 is thrown forward by the contact of the 

 projectile, this teat is withdrawn from the 

 hole in the percussion pellet, releasing the 

 percussion spring. This throws the per- 

 cussion pellet forward forcibly, resulting in 

 the contact of the percussion needle with 

 the second detonator. The flash created 

 is transmitted through the flash holes 

 surrounding the needle and passes to the top 

 of the gaine tube, thus doubly assuring ig- 

 nition of the explosive charge in the shell. 

 This second detonating arrangement can 

 not operate until the graze pellet has been 

 thrown forward into contact with the 

 graze needle, and the graze pellet cannot 

 travel forward until the centrifugal bolt 

 has been thrown out of place, which, in 



419 



