The trials were carried out on the sands just east of Calais over the ground used by the French for their own artillery experimental firing.
The ground was somewhat unsuitable for the erection of wire entanglements as there was only the sand available, and in some parts it was damp.
The battery consisted of four guns in position amongst the sand dunes with the trails supported on sandbags. The gun platforms, therefore, though only indifferent were not sufficiently so to affect the shooting adversely.
Targets.The targets consisted each of two rows of wire entanglement, separated by a space of 10 yards, each row being 20 feet deep. Ten yards in rear of the second row was a parapet built up of sandbags 4 feet 6 inches high in the centre and 3 feet at the ends and about 10 feet thick: Targets 1, 2, 4 and 5 had a parados behind the parapet. Targets 3 and 6 were open at the back. The frontage of each target was 20 yards.
There were three targets arranged side by side at each of two ranges, namely, 2,700 yards and 3,400 yards.
During the first three series fire was stopped in each case after 60 rounds for the purpose of examining the targets. Fire was then continued up to 120 rounds for each series, except in Series 3, in which fire was not continued after 60 rounds.
For the 4th, 5th and 6th series 150 rounds each were allowed and no pause was made for examination of the targets.
Series l. After the first 60 rounds a few posts were broken and strands of wire cut, but there was no practical diminution of the obstacle as a whole.
After the series was completed there was a narrow path through the front strip of wire about 2 yards wide and through the rear strip about 5 yards in width.
Six sandbags were thrown down into the trench. About 50 per cent. of the rounds burst on graze. The principal damage to the entanglements appeared to be caused in each case by a well pitched percussion shrapnel.
Series 2.In the first 60 rounds there was practically no effect obtained.
After completion of the series there were some six or eight posts broken and a few strands of wire cut, but no important damage done; as a wire cutting series it was a failure.
There were four detonations in the first entanglement.
There were three detonations in the second entanglement.
There were four explosions in the second entanglement.
There were four sandbags blown down into the trench.
Series 3.As in Series 2, except that there was practically no effect against the wire, which was almost untouched.
Twenty-five rounds burst on graze; 35 burst after graze at an average height of 14.5 feet.
Eleven hits on a canvas screen stretched on the ground behind the parapet. 11 sandbags knocked down from the parapet. No hits on some boxes placed close under the parapet.
Series 4. No pathway was made through the wire and very little of the entanglement was in any way disturbed.
Many of the shell were burst at a suitable height just short of the target. The shooting was in no respect erratic, but the guns might have shot better together.
Series 5.The entanglement was undamaged by the fire.
Eleven sandbags were knocked down into the trench.
Seven shell had detonated and 7 exploded in the first entanglement.
One shell had detonated and 5 exploded in the second entanglement.
Series 6.The entanglement was undamaged by the fire.
Thirty-five per cent. burst on graze.
Fifty-eight per cent. burst after ricochet at an average height of 16.1 feet.
Eight per cent. were blind.
Three of the boxes placed behind the parapet were perforated by splinters.
The boxes were not so close to the parapet as in Series 3.
There were 35 hits on the canvas on the ground behind the parapet.
Eight sandbags were knocked down from the parapet.
One shell had detonated and six had ricochetted in the first entanglement, and seven shell had ricochetted in the second entanglement, but no shell had detonated in the wire.
About 75 per cent. of the H.E. were filled Amatol and 25 per cent. with. Trotyl.
The blinds amounted to about 5 per cent. of the whole of those that burst.
No. 85 Fuze.
The principal objects in view were
As regards the first of these objects, the experiment conclusively proved the superiority of the 18-pr. shrapnel over H.E. burst on percussion for cutting wire.
It also showed that the H.E. overs that missed the wire and insufficient effect on the parapet to make it worth while to use H.E. for wire cutting with the subsidiary object of damaging the parapet at the same time. It is clear that damage to defences of any strength can only be obtained with 18-pr. H.E. by an accurately ranged and concentrated fire.
The greatest effect produced on the wire was by percussion shrapnel, and it is not unreasonable to infer that the best effect may often be produced by choosing a corrector that will give from 50 to 75 per cent. of grazes. It was clear also that the effect on the wire varies considerably with the range. It is, therefore, not possible to lay down that wire can be cut with so many rounds per yard.
There are other factors that come in, such as the strength and extent of the obstacle, the contour of the ground, the facilities for observation, the skill of the Battery Commander and the service of the guns. It is perhaps safe to say that if the range is over 2,500 yards a considerable increase in the amount of ammunition will be necessary, and it should be a rule that if it is intended to follow up the wire-cutting by an attack the fire should be con-tinued till the object has been satisfactorily attained.
Ammunition will be saved if each gun is carefully ranged before opening fire for effect.
The experiment was not intended to demonstrate the value of any particular method of fire for wire-cutting, and nothing of value was learnt in this respect.
As regards the second object, the general impression gained of the H.E. with No. 100 fuze and gaine with delay was fairly satis-factory, but allowing for the fact that some of the shell were caught by the parapet and some in the rough sandhills beyond, the percentage that burst after ricochet was not as high as had been expected. The number of hits on the boxes and canvas showed the downward effect of the burst. Shrapnel bullets could not have reached either the boxes or the canvas, and it is a fair con-clusion that this projectile is more effective against infantry in trenches, and therefore preferable to shrapnel for retaliation, and on any occasion when infantry can be compelled to man their parapets.
The impression was also gained that this projectile would be effective if mixed with shrapnel for repelling an attack or for barrages.
The superiority of Trotyl over Amatol was most marked, at any rate with the present method of detonation.
A note is attached on the comparative value of H.E. burst in the air with time fuze and burst in the air after ricochet, but this question was not tested at the experiments.
72nd Battery, R.F.A.
Probably these guns have all fired some 6,000 rounds each previously.
Shell with No. 85 fuzes.
Shell with No. 100 fuzes.
Shrapnel shell Mark V.
NOTE ON THE USE OF HIGH EXPLOSIVE SHELL FOE FIELD GUNS.
H.E. shell for 13-pr. and 18-pr. guns may be used in three different ways :
H.E. shell will eventually be issued to batteries at the rate of 50 per cent. of the whole equipment. Of this number about one-half will be fuzed with No. 100 fuze with .04 second delay, and one-half with a T. and P. fuze.
It is of great importance that officers who have to use this ammunition, and who have not had much experience in testing the comparative effect of the different kinds of fuzes, should be well acquainted with their possibilities, in order to be able to suit both the nature of ammunition and the method of its use to the occasion.
The value and use of shrapnel are well known. A hard hitting heavy shrapnel shell depends for its effect on its forward sweep. The shrapnel is, therefore, always burst in front of or short of the objective.
With H.E. the case is different. The forward effect is practically nil. The force of detonation acts in a radial direction at right angles to the longer axis of the shell. The forward sweep is entirely absent. If burst in the air the shell must burst over the target to be struck. If the shell were, horizontal it would need to be vertically over the objective. If the shell is falling, and therefore with its longer axis inclined downwards, the effect will be partly backward, as with the German H.E. shell with a time fuze. If the shell is rising at the moment of burst as with a ricochet similar to the French, the effect is slightly in a forward direction. This radial action of the wave or force of detonation is known as the cart-wheel effect, and is common to all H.E. shell.
As with our equipment we are in a position to obtain bursts not only on percussion but in air, either with a time fuze or with a ricochet fuze, the characteristics of the two methods of obtaining air bursts are worth consideration :
With delay action fuse.There are two factors affecting the accuracy of shooting or possibility of bursting the shell in a position suitable for hitting the objective, they are :
The Calais trial showed that the latter is very considerable, the bursts taking place at heights varying from about 1 foot to 40 feet, representing a horizontal distance of about 50 yards at a range of 3,000.
Added to this, however, is the error of the gun, and the 100 per cent. zone with the 18-pr. at 3,000 yards is about 120 yards.
It will be seen, therefore, that to obtain hits on men in a trench under cover of the parapet a large number of rounds would have to be fired, for it would be necessary to obtain a burst almost vertically above such a narrow target in order to obtain effect.
A further difficulty in dealing with this nature of fuze is the limitation which is imposed by the nature of the ground in front of the target. The action, of the fuze is dependent both on the surface of the ground and the slope which affects the angle of incidence of the shell. A ploughed field or any rough or boggy ground will add considerably to the number of shells that fail to ricochet, whilst the slope of the ground, if towards the firing point, has the same effect.
Finally, the range also has a direct bearing on the percentage of failures to ricochet that may be expected.
The figures for ordinary firm level grass land are as follows :
The critical point is when the angle of arrival is about 10 degrees.
These favourable conditions, however, are rare, and too much, therefore, must not be expected from fire undertaken with this type of ammunition.
H.E. with a time fuze.With this nature, the conditions to be fulfilled are very different.
Ability to obtain a burst in the correct position depends mainly on the error of burning of the fuze once the range has been found.
All that is necessary is to range until the mean point of impact passes through the objective, then raise the angle of sight by the amount it is desired to burst above the target (say 5 minutes) and obtain the correct length of fuze by alteration of corrector setting in the usual way.
It will be seen that the error of the gun and inequalities and slope of the ground are factors which do not then count.
The error in burning of the fuze is the only variable directly affecting the result, and as all shell should burst in air, except the necessary percentage on graze, the effect at entrenched infantry is likely to be at least as favourable as in the case of delay action fuzes.
When it is further considered that the range has no effect on the H.E. with time fuze, it is probable that the balance will usually be in favour of the employment of this nature in preference to the delay.
For the purposes of barrage fire or shelling areas, roads, &c., when it is desired to combine H.E. with shrapnel, there is less objection to the characteristics of the ricochet fuze, as its action will then be to cause the shells to be distributed over a certain space in depth, whilst at the same time the cart wheel action is produced at each point of burst in turn.
If used against buildings, the ricochet fuze would burst the shell about 40 or 50 feet in rear of the first part of the building struck, and probably the effect would be lost. A percussion or T. and P. fuze designed to burst on impact with the house would be more suitable.