360 Sir Robert Robertson [May 6, 



The Land Service High Explosive Shell. 



The problem of bringing trinitrotoluene to complete detonation 

 with certainty had been worked out some years before the war. The 

 type of shell to be described was used by the Land Service, and 

 contains the results of developments mostly made during the war. 



Prior to the war the Land Service used for the most part shrapnel 

 shell, designed to project a shower of lead bullets, efficacious against 

 personnel, but of little value in attacking fortified positions, for which 

 high explosive shell is required. 



Shrapnel was very largely used by the Land Service throughout 

 the war, but the earlier type of high explosive shell filled with lyddite 

 (picric acid), and brought to explosion by the ignition of a fiercely 

 burning mixture, was abandoned for one in which true detonation 

 was secured with certainty. The latest type of high explosive shell 

 was exemplified by a 4*5 in. howitzer shell fitted with a graze fuze 

 (Fig. 1). 



Fig. 1. 



The Fuze. — A graze fuze is a mechanism which gives rise to a 

 flash when the shell grazes on the ground. It must be capable of 

 being handled roughly without firing, and must not act when the 

 considerable forces involved in firing it from a gun are impressed 

 upon it and upon all its parts. The magnitude of these forces is 

 illustrated by the fact that a fuze weighing 2£ lb. when fired from 

 an eigh teen-pounder gun weighs about 11 tons — the stress correspond- 

 ing to 15,000 times the acceleration due to gravity. These forces 

 are taken advantage of to render the fuze " live " — that is, to put it 

 into a condition when it will act on the slightest provocation. 



In the interior of the fuze is a brass cylinder with an axial hole, 

 on the top of which is placed a capsule containing a highly sensitive 

 flash composition. To prevent this cylinder from moving forward 

 in handling, a bolt lies athwart its top edge, and this bolt is retained 

 in this position by a small pin placed vertically at the back of the 

 bolt and having its base pressed upward by a spring working in a 

 vertical cylindrical cavity. On firing, this pin, weighing 1 ■ 3 grams, 

 is acted on by a force equivalent to 20 kg., overcomes the resistance 



