Artillery

[nicburch]

Hello all,

Can anyone explain in layman's terms about the evolution of predicted artillery fire which i believe was first used at Cambrai.

[johnreed]

Predicted Fire.Is a form of fire in which previous firings to adjust the fall of shot onto the target has not been carried out.

i.e. If you know the grid reference of the intended target and the gun position grid is accurately plotted you can with a certain degree of accuracy calculate the bearing and range or QE to the target for the guns to engage.

does this make sense.

John

[Robert Dunlop]

The evolution of predicted fire is quite interesting. It bought together several developments. Firstly, the growing awareness of the need for sudden 'hurricane' (ie very heavy) bombardments as opposed to prolonged softening up. This had been used at Neuve Chapelle in 1915 to great effect. But the right lessons were not learned and prolonged preparatory bombardments became the norm. These aimed to destroy the enemy but, as July 1 1916 showed, good defences could negate this. The success of attacks such as July 14 1916 (Battle of Bazentin Ridge) began to reinforce the value of sudden (relatively - there was still an element of preparatory artillery fire) pre-assault bombardments with the aim of suppressing rather than destroying the enemy. It took quite a while before infantry commanders would accept the value of this type of bombardment.

Meanwhile, German defences became less linear and more porous. The depth increased to several miles. Multiple pillboxes, blockhouses, strong points and other defensive features were used to dominate ground. Trenches served as protected walkways rather than the dominant defensive structures. The creeping barrage, which really came to the fore in 1917, enabled infantry to follow the barrage. Obviously, the very wide wall of shells of various calibres would suppress the enemy, so long as the infantry could keep pace with it. However, it did churn up the ground and it was difficult for tanks to avoid the barrage if they were at the forefront of an attack.

In parallel with these developments was the growing realization that absolute surprise held the key to a successful action. Creeping barrages were highly complex to orchestrate. Gunners had to know precisely where their shells would land. If they registered their guns on the battlefield, ie fired some shells at known targets and observed/corrected the fall until the shells were on target, then the Germans would become aware of the guns. As artillery gun barrels became worn, there was a greater tendency for shells to wander from where you were trying to aim. Each gun was idiosyncratic in this respect, so all guns had to be tested in some way. The key was to find a way to test the guns without needed to register them on the battlefield.

Two techniques (that I know of) were used. One involved the use of sound-ranging equipment. This could provide information on the muzzle velocity of the gun. The other involved firing the gun on a target range and observing what happened. When the behaviour of the gun had been calculating, the information would be kept with the gun. It would enable the gunners to calculate how the gun would perform under different wind and atmospheric conditions as well.

Now it became possible for the guns to be bought into line and only fire when the barrage started, thereby attaining complete surprise. It also meant that instead of firing a continuous wall of shells that gradually moved forward, covering everthing in its path, it was now possible to target the various defensive positions. This left the intervening ground untouched, making it easier for tanks and infantry. Tanks were a vital ingredient because they could take care of any wire, which previously had to be 'cut' with artillery and Stokes mortars. And it all came together at Cambrai. Subsequently, it was difficult to get everyone to accept that it was going to work again. So the Australian infantry were less than enthusiastic about predicted fire being used at le Hamel for example.

Predicted fire became less feasible during the constant advances of the last 100 Days. Guns were constantly in action, with little time to prepare for predicted fire. The ability of the guns to support the infantry was still extremely impressive at this time.

Robert

[johnreed]

Robert. I have just one or two observations to make firstly you will never be able to calculate the MV of a gun by sound ranging. The best way at that time to work out the MV of a gun was by fall of shot calibration which in itself was a long drawn out process and could never be done on the battlefield. At that time the best way of working out the MV's was by the meticulous recording the record of rounds fired and working out the EFC's (Equivilant Full Charge). The barrel will be given a life of so many EFC's, don't forget that barrels are rotated at quarter life to even the wear at C of R.

John

[nicburch]

Robert and John, thankyou for your explanations,although i am a little confused about sound ranging.

[Robert Dunlop]

Oberon, the technique of sound ranging was an important advance in the detection of enemy guns.

Sound ranging had started in the French and German armies. It consisted of listening posts or microphones arranged behind the frontline. These were based at known positions, which recorded the time when a gun report was heard. When the timings were compared from all of the posts, it was possible to calculate the epicentre of the sound wave ie. the location of the gun.

The British initially studied the French systems. The timing of the gun report was recorded in several ways:

i) observer pressed a key. This was associated with a split second delay between the hearing of the sound and the pressing of the key. It was a simple system and some allowance could be built in for the human delay. This worked well for guns that were close to the observer. The timing errors became too large when guns were firing at longer ranges.

ii) sound was recorded by stylus on paper, activated by the electrical currents from the microphones.

iii) use of galvanometer, which caused displacement of fine wires in the strong magnetic field. The movement of the wires was captured on cine film - a strong light shone across the wires, through a slit and onto the moving film strip. The system was switched on by forward observers who heard the gun before the sound wave reached the recorder. The film was quickly processed and then various sound 'spikes' could be measured. This allowed greater accuracy in location of the firing gun. The whole was known as the Bull system, named after Lucien Bull of the Institut Marey, Paris. The Bull system was refined but in trials in 1915, guns that were 4-6 km away could be fixed within a 5-25m margin of error. Eventually, there were at least 50 sections that were reponsible for covering the British front. Sound ranging units were also deployed in the Middle East and in the Balkans.

A major problem with sound detection was noted in 1915. The electronic systems could pick up high-frequency noises but not the low frequency 'muffled boom of a gun going off'. During flight, the high velocity guns would generate a loud 'crack' as the shell reached mid-flight, followed by the low pitched boom of the gun. The former was easily detected but the latter was important for actually determining the location of the gun. The French devised complex curves that could link the shell-wave and gun report timings. However, this proved too complex.

The next big advance came when it was realised that, while it was difficult to hear the gun fire, the pressure changes were readily felt. These changes would rattle glass windows for example. It was further noted that in cold weather, a blast of cold air would come through any little cracks in the wall of a house after a gun fired. This led to an ingenious system where air was directed through a small aperture onto a hot Wollaston wire. This cooled the wire, altering the electrical resistance and triggered a 'quite characteristic and definite large break (in the baseline recording) which could be read with accuracy'. The size of the deflection would indicate the calibre of weapon being fired. This became known as the

Tucker microphone, named after Corporal Tucker, a physicist.

Wind was a problem because it would spontaneously cause fluctuations in air pressure. Solid walls or shelters made this worse. However, hedges or layers of camoflage netting rigged in front of the apparatus served to dampen the pressure fluctuations. 'It is interesting to note that (the Germans) could not understand how we avoided the wind trouble, which seems to have defeated them completely when they tried out our method.'

Further improvements resulted from placing the microphones in an arc, 'with its centre roughly in the most interesting area behind the enemy lines'. Also, the use of temperature and wind data made for improved corrections. Ultimately, Tucker microphones could be used to 'record almost any number of guns firing at once'. They were used to help calibrate the British guns as well.

'The great drawback of sound ranging is that it fails when the wind is blowing away from our lines... not only is the sound faint but it also has an irregular beginning'.

Taken from 'Sound ranging in France 1914-1918' by Sir Lawrence Bragg (annex in Farndale's book on the RA)

John, I have highlighted the text that I intepreted as related to this issue of calibrating British guns.

Robert

[Robert Dunlop]

Monash described a technique for calibrating the artillery before the Battle of Amiens:

"This method... consisted of the firing of the gun through a series of wired screens, placed successively at known distances from the muzzle of the gun. The whole elements of the flight of the projectile could then be accurately determined by recording the intervals of time between its passage through the respective screens. From these data could be deduced the muzzle velocity, the jump, the droop and the lateral error of each gun."

Robert

[johnreed]

Robert I think that you have slightly got the calibration of guns slightly out of context. In a normal sound ranging senario there is no way it could be used for calibration of Artillery pieces, but with microphones and the use of a Bull recorder and wire screens it was possible to record with accuracy the time between the breaking of wires in the screens through which the shell was fired. This system was still in use at PEE Shoeburyness to my knowledge in 1970's. By the way I spent 27 years in the RA, 10 years in a RHA unit where I participated in Fall of Shot Calibration (A long and tedious process) EVA Calibration using a Marconi Electronic Analyser( A system which is based on the Doppler Radar). I then spent 17 years in a Locating Regt, guess what it had three Sound Locating Troops, but I Commanded a Meteorological Troop.

Regards

John

[Robert Dunlop]

I think that you have slightly got the calibration of guns slightly out of context.

Thank you for the extra information, John. I am only able to reproduce the information as given in the text. The extra detail is not available there so it is very helpful to receive your clarification. Presumably, this is what Sir Lawrence Bragg was referring to in his article.

Robert

[johnreed]

Yes that is correct, here is something that you might find interesting it is a sound trace on 11-11-18 at 1100 hrs.

John

[Robert Dunlop]

One or two coughs after the 11th hour but nothing serious Thanks for that.

Robert

[johnreed]

Perhaps a hangfire ??

John