Updated 24 January 2014





     Sound Ranging
     Flash Spotting


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Originally in World War 1 (WW1) the British Army had created, from almost nothing, a formidable capability to defeat their enemies’ artillery.  By 1917 the lynch-pin of this capability was the Counter-battery Staff Officer (CBSO), an artillery lieutenant colonel, assigned to each corps.  He and his small staff were responsible for collating and analysing all information about enemy artillery, and controlling counter-battery (CB) fire.  Depending on the circumstances the purpose of this fire was to either destroy or neutralise the enemy’s batteries.  The primary sources of information were air reconnaissance, particularly aerial photographs, by the RFC (and RAF), sound ranging and flash spotting.  By the end of the war each forward corps had a brigade of six RGA batteries dedicated to CB work, with other RGA and RFA brigades and batteries used when necessary and available.

In August 1919 the War Cabinet provided post-war strategic guidance:

The implication was that there was little or no requirement for a counter-battery capability.  Britain rapidly de-mobilised and the size of the army shrunk dramatically.  This policy was modified in 1927 to no European War for the next 10 years, but army plans were to include preparedness for a war outside Europe.  In the early 1920's Turkey and Afghanistan were seen as potential threats to British interests.  In the 1920's this ‘strike force’ preparedness was planned as a mobilised regular army force of six divisions (including one cavalry), presumably organised in two corps as was the 1914 BEF.  Of course the corps HQs were ‘shadow’ organisations and not permanently formed, and hence untrained as field HQs.

Another important issue was a doctrinal emphasis on mobile warfare, although it was also recognised that there would be periods where there would be a stable front.  Mobile warfare posed major problems for CB, the deployment time for sound ranging and flash spotting was one issue.  However, it also meant that the dwell time of HBs could be short and this would prevent CB intelligence from having a reasonably complete and stable 'picture' of the enemy artillery deployment, which would make a successful CB battle difficult.  Mechanisation was edging forward as financial constraints permitted, and by the late 1930's the British Army was almost entirely horseless.  However, the counter-battery battle in mobile warfare was a challenge without any easy answers.

There was an additional factor affecting counter-battery.  In the 1920's the new RAF survived Admiralty and War Office challenges to its independence.  However, its survival was due mainly to Trenchard’s advancement of strategic bombing as its primary role.  This inevitably meant that support to the Army became a very secondary priority.  It's significance was reduced further by RAF involvement in the developing UK air defences in the later 1920's and 1930's.

Nevertheless the three main aspects to CB, established during WW1, were continued:


There were four counter-battery elements:


During the war it had been recognised that sound ranging, flash spotting and artillery survey should be the responsibility of the Royal Artillery not the Royal Engineers.  To this end a Survey Company RA was formed at Larkhill and named 1st Survey Company in 1922.  By 1938 it comprised X, Y and Z Survey Sections, and one section each for Flash-Spotting (FS) and Sound-Ranging (SR).  The company deployed to Turkey in 1922-3 as part of a larger British force, in response to rising tension and the Chanak Incident.  They spent their time with 1st Corps Topographic Section undertaking a plane table survey of the Gallipoli Peninsula.  None of the other campaigns of the interwar period needed their capabilities. 

A survey section was formed in India in the 1920's and continued until the outbreak of war.  However, it does not appear to have had any flash-spotting or sound-ranging capabilities.

SR and FS Sections were formed at Cambridge and SR at London University Officer Training Corps in the early 1920's.  TA companies formed at Bristol and Gateshead in the 1930's, Bristol being converted from Royal Signals in 1934 to become 3 Survey Coy.  Gateshead formed in 1937 and became 4 Survey Coy, both had with close links to Bristol and Durham universities respectively.  By 1938 3 and 4 Companies each had two survey sections, a FS section and a SR section.  In late 1938, the companies were expanded into regiments and on mobilisation each regiment spawned another regiment.

Although they were formally named ‘sections’, in accordance with established artillery nomenclature, it appears that colloquially the WW1 term ‘Groups’ remained in use for the FS element in a survey company.  A FS section, commanded by a captain, comprised an HQ (plotting centre) and 4 (6 after mobilisation) OPs.  The SR section was as it was in WW1, a plotting centre, unmanned microphone base and two Advanced Posts to alert the plotting centre to switch on the recording equipment.  Both sections were required to cover a corps front, and had their own line laying capability to provide communications between observers, microphones and plotting centres.

At some point the Corps HQ organisation (although there was no established corps HQ, it was a 'shadow' organisation) changed, the position of Corps Heavy Artillery Commander became Commander, Corps Medium Artillery (CCMA).  This reflected the fact that there was very little heavy artillery.

There is one other point, the neglect of mortars.  After WW1 mortars went out of service and did not re-appeaar until two 3-inch mortars were added to infantry battalions in the late 11930s.  In contrast the German army had six per infantry battalion.  The lack of mortars led to them being ignored as a potential counter-battery target and the need to locate them.  This was to become a very significasnt problem in WW2.


In the post-war RAF the army support role undertaken by corps squadrons for the army in WW1 became ‘Army Co-operation’.  It was also recognised that fighter squadrons could attack ground targets in support of the army.  The 1920-21 budget allowed one Army Co-operation squadron, the Army Co-operation School at Old Sarum, the Balloon School at Larkhill, and a Photography School at Farnborough.  In 1923 four more Army Co-operation squadrons were authorised and subordinated to the new 22 (Army Co-operation) Group, an Air Commodore’s command, in Air Defence GB and later Fighter Command.  By 1935 these five squadrons were to support an expeditionary force of up to six divisions.  

Their role was much the same as that of the corps squadron in WW1. Field Service Regulations Vol 2 Operations (FSR) 1924 defined it as:

FSR 1929 stated that an Army Co-operation Squadron was under command of the army formation and modified the roles slightly to:

FSR 1935 added dropping small quantities of supplies to the list. 

Army Co-operation squadrons had two attached air liaison officers (ALO) from the army, their job was to brief pilots before they flew.  Upon their return the ALO de-briefed them, investigated their reports and ensured that information was communicated rapidly to the formations and units concerned.  The RAF was responsible for taking, developing and printing air photographs, the Army for plotting, interpreting and distributing them.

However, both army and RAF officers tended to do only one tour in army co-operation, which was probably less than entirely satisfactory from the perspective of developing skill and experience.  Furthermore, while there the RAF officers were often sent on courses unrelated to army co-operation.  It was not an arrangement conducive to developing skills and gaining the insights necessary to adapt to the evolving land-air environment.


In 1924 the RFA and RGA were merged to form RA.  In 1929 there were seven regular army medium brigades totaling seven batteries of 60-pr Guns and 21 of 6-inch Howitzers, all used vehicles for towing guns apart from two batteries in India.  There was also a single heavy brigade of four batteries with 6-inch Guns and 8-inch Howitzers.  Other heavier guns and howitzers from World War 1 remained in store.  In 1938 medium brigades were re-designated as regiments and reorganised from four batteries of four guns into two batteries each with two troops of four guns.

The Territorial Army (TA) had a further 11 medium brigades in 1929 but by 1938 had been reduced to nine.  Later in 1938 the TA was doubled in size by forming new units, TA medium regiments doubled in number.



Field Service Regulations (FSR) Vol 2 Operations established the military doctrine.  The 1924 edition stated that CB was an important part of the artillery plan, with the objective of neutralising all hostile batteries (HBs) that could impede infantry and tanks.  CB was to be continuous in defensive operations but with no unusual activity before an attack.

The 1929 edition of FSR stated that in defence CB was generally under corps control.  The commander would issue instructions for the general direction and policy for CB, the activities of corps medium and heavy artillery, allotment of zones of fire and for RAF calls for fire, and policy on ammunition expenditure.  In defence HBs would be located by air photography, flash spotting and sound ranging and engaged when enemy artillery preparation fire started.

Field Artillery Training (FAT) Volume 2 Gunnery, 1921 (Provisional) and the 1928 edition had little to say about CB and nothing about its organisation.  However, in 1928 the new FAT Vol 3 Organisation and Deployment, Chapter V, provided organisational doctrine on the lines developed in WW1.  The task of CB was to locate, neutralise and destroy enemy artillery.

FAT Vol 3 also stated that the form and importance of CB at any particular time would be decided by higher commanders, noting that offensive CB had the disadvantage of disclosing own positions and driving HBs to unknown positions.  It suggested that for maximum effect it may be better for active CB to be applied only at decisive phases.  All batteries needed to be prepared to undertake CB.

The Major General RA (MGRA), presumably of an expeditionary force, was responsible for CB co-ordination including defining the corps artillery air reconnaissance areas.  The Commanders, Corps, RA (CCRA) formulated CB policy within the MGRA’s limits and defined divisional artillery air reconnaissance areas in consultation with the General Staff and the RAF Wing Commander (implying that the Army Co-operation squadrons were grouped into a wing for each of the two expeditionary corps). 

The corps medium artillery was commanded by the Commander, Corps, Medium Artillery (CCMA).  His staff included the Corps Counter Battery Officer (CBO) and his staff of two other officers and various specialist soldiers.  They were part of the CCMA’s HQ with the CBO working alongside the Brigade Major Medium Artillery.  This HQ was supposed to be as near to the FS and SR sections as possible, an interesting proposition for an expeditionary force of two corps and only one survey company with one section each of FS and SR, but mobilisation may have created a second company. 

In principle control of CB was to be centralised at the highest HQ that could exercise it without risk of failure.  When corps control was impossible divisions were to undertake CB with available assets including medium artillery under divisional command.  CBO staff would temporarily join divisions, typically during mobile operations.  The issue of CB in mobile operations was a persistent theme throughout the period, the main problem being the time it took to deploy SR and FS, particularly the line laying effort, although the time need for artillery survey was also an issue.  If anything these difficulties increased dependence on air reconnaissance.

It was also recognised that it would seldom be possible to have dedicated CB artillery (as had been the case in 1918).  Furthermore, there was no suggestion the CBO would have ‘executive control’ of CB fire as had been the doctrine established by GHQ Artillery Notes No 3 at the beginning of 1918.

The duties of the CB staff were to locate hostile artillery, provide information to the CCRA, CCMA, divisional CRAs and flanks, draft orders and instructions for dealing with and engaging HBs, arrange army co-operation aircraft for artillery and photographic reconnaissance and the RA survey company, and arrange mutual assistance with flank formations.

The recognised sources of CB Intelligence were:

A FS base was up to 10,000 yards long, an 8,000 yard base needed 10 miles of telephone wire.  It took 4 – 8 hours to lay line and survey OPs, although observation could start immediately an OP deployed.  FS could only observe HB flashes at night.

Intelligence collection had to be continuous, results recorded systematically and in as great detail as possible.  CBO was to prepare maps of HBs and shelling connections.  

Continuing WW1 practice, CB fire was either destructive or neutralisation.  Neutralisation was to prevent enemy batteries firing for the time being and reduce efficiency through casualties and lowering morale.  In defence neutralisation would provide relief from enemy bombardment.  When flying was possible neutralisation would be adjusted.  In positional warfare concentrations (ie of several batteries) were recognised as a valuable method, particularly when observation was limited or there were several HBs in a small area. 

Destruction shoots were against materiel – ie the guns themselves, but were rarely possible in mobile warfare.  Destruction needed a large amount of ammunition, accurate ranging with steady and systematic fire usually with air observation.  They were not usually effective against personnel but impromptu air observed shoots were efficient when time and ammunition were available.  Some authors considered that concentrations with the purpose of causing casualties and some damage on the gun position were a third option, the expectation being to impose a cost on the enemy by disrupting, delaying and degrading their capability..

General artillery intelligence was separate from CB intelligence, but both dealt with information about enemy artillery.  Artillery intelligence officers were at Army HQ, corps HQ and CCMA, staff lieutenant at division and the assistant adjutant at each artillery brigade (ie regiment).  Non-CB artillery intelligence came from the same information sources as for CB but was used to produce information about the enemy artillery order of battle, intentions, capability and other more general intelligence purposes.

Also recognised was a need to be ready for war in undeveloped countries.  This meant inadequate maps and no local map grid.  Lack of a common grid would make predicted fire, concentrations, sound ranging and flash spotting extremely difficult but not totally impossible.  It would make air observation even more important.  During the period developments in photogrammetry were making mapping cheaper, quicker and easier so the number of poorly mapped areas was decreasing relatively quickly.


By the mid-1930's the various elements of the CB system did exercise together, and an effort was being made, judging by articles in the RA Journal, to educate the new generation of artillery officers in CB matters.  Map shooting was generally included in live firing training and there were prescribed target dimensions that were marked out in the range impact area to enable its accuracy to be judged.  However, the mean point of impact of map shooting was usually about 50 yards from its aimpoint.  Given the size of training areas in UK the firing distances would have been relatively short and inaccuracy is magnified by longer range, then there was clearly room for improvement. 

It’s unlikely that survey was a problem given that firing was on training areas where survey control points were relatively plentiful.  Calibration may have been a problem because financial pressures restricted the amount of ammunition available for it.  However, limited firing also meant there would be little barrel wear and short firing ranges meant low charges with negligible wear so frequent calibration was unnecessary.  Meteor data used to calculate the corrections for non-standard conditions is another possible source of error.  However, the Meteorological Office provided data to training areas, and the short ranges and hence low trajectories meant that the methods used to capture meteor data were probably satisfactory. It should also be remembered that range could only be set on gun’s sights to the nearest 25 yards. 

Ideas emerged from 1st Svy Coy for integrating SR and FS, one with obvious attractions from an economy of effort perspective was to site a SR microphone near each FS post.  Of course this was not really a practical proposition given the different siting requirements of the two.

FSR 1935 stated that CB was to neutralise or destroy enemy artillery and was usually carried out by medium and heavy artillery with air observation.  It was generally under corps control, communications permitting.  Air photography, FS and SR were the main sources of target information and HBs were to be engaged when enemy preparation fire started.  The thinking behind this was that if CB fire was too early then HBs would move and have to be found again.  

A 1932 amendment to FAT Vol 3 added a new Chap XII that introduced standard plotting and map marking symbols for CB and various forms.  These were: Form B 99-4 for shelling connection activity records, CB Chart, Concentration traces, Form B 99-5 a blank grid, Form B 99-6 HB Activity Sheet, and guidance on deciding CB policy.  It also formally introduced three categories of HB - Fixed, Unfixed and Suspect.

FAT Vol 2 was replaced in 1934 by Artillery Training Vol II Gunnery, the focus was on gunnery methods and practices not those for CB.  It did not explicitly mention CB but in the chapter ‘Methods applicable during periods of stabilization’ dealt with CB relevant gunnery procedures:

The chapter Co-operation with RAF stated the following, almost unchanged from WW1 practices:

It also recognised three types of call for fire by an air observer: OE (single battery, ranging by single rounds), FG (single battery, ranging by groups of rounds) and LL (a heavy concentration of fire).  For moving targets observers reports target location in 4 minutes, implying that this was the expected speed of response from the medium or heavy battery.

Wireless telegraphy, continuous wave using Morse code, was used for air to ground communications, it remained a one way communication channel.  Telegraphy required use of the two and three letter Artillery Code that had started in WW1.  Ground to air communications was by white strips placed to form single letter or symbol.

An RAF wireless station with RAF operators was to be deployed to each medium and heavy battery, although it appears that in peacetime they were in the army co-operation squadrons.   The battery commander had to give the RAF signallers signed orders on RAF Form 776 Battery Operators Card about what calls to listen for, the Zone Call system was still in use although zones were now defined by map co-ordinates. 

A new series of Artillery Training Volume 1 pamphlets were issued in the late 1930's.  Pam 5, 1938, Information, Reconnaissance, Local Protection and Ammunition Supply, included ‘Sources of information’, in essence unchanged from WW1:

Of particular importance for CB was Pam 7, 1938, Duties of the Counter-Battery Staff and Recording of Information.  General points were as follows:

It required there was to be continuous collection and collation of CB information, results recorded and easily accessible so that:

It continued the policy that CB fire was to neutralise or destroy HBs, and was normally centralised under the CCMA but could be decentralised in mobile operations.  CB had to be considered when planning Covering Fire, Defensive Fire and Counter-Preparation Fire. 

Specific CB Duties were detailed as follows:

The captain and lieutenant, each with a clerk, were detached to divisions when CB control was devolved.  It also noted that during prolonged fighting it might be necessary to increase CB staff.

Pam 7 identified the following records:

In mobile operations there would be less information, basically the CB Log and HB History sheet, there would seldom be time for full indexing of air photos.  The CB chart was essential but with less detail, and CB summaries and HB lists would be issued.


Sound Ranging

Initially the sound-ranging equipment was unchanged from the previous war.  Both the recording and microphone components were fully described in the Handbook of the Sound-Ranging Instrument, 1921.  In the 1930’s a new microphone was introduced, unfortunately it did not offer any notable improvements and appears to have been incorrectly manufactured.  However, in 1931 a new recording system was issued, (Recorder, SR, No 1 Mk 1).  It continued the use of a multi-string galvanometer and capturing its vibrations on photographic film and included film processing.   It was a single unit that could be mounted in a truck or dismounted, but needed at least two men to manhandle it.  

There were other changes to the equipment that generally increased its weight and did not provide any obvious improvements in performance.  Less useful was a mechanical plotter (Plotter, SR, No 1) to replace the simple plotting board and its ‘time of arrival difference scales’.  The original requirement was for three dimensional plotting, but this proved too difficult and a two dimensional device was developed.  It is not clear if this device made it easier to plot observation of own artillery fire and correct it onto a hostile battery.  Only one example of the Mk 1 version seems to have been produced in 1934  and was issued to 1st Survey Company for trials, many improvements were recommended.  

However, before a Mk 2 could be produced another good idea emerged - the possibility of using a manual mechanical calculator of the Brunsviga type.   Several companies and individuals got to work, but eventually the effort was abandoned due to the impossibility of resolving the equation  without many manual iterations, which offered no advantage over other methods.  It is unclear if a Mk 2 version of the Plotter was ever produced.  However, one important device was introduced in the early 1930's, the first comparator.  This was used, when ranging own artillery, to calculate the correction  from the located fall of shot to the target hostile battery (or other point).  There were some limitations on the use of the comparator due to constraints on the geometric relationship and distances between target, guns and the sound ranging base. 

Also developed were three different patterns of microphone windshield, including a beehive shaped structure several feet high.  These devices comprised a metal frame covered in coconut matting.  Eventually the flattest one was adopted and remained in service for several decades.

These various devices did not impress Professor Sir Lawrence Bragg, who considered the main effort should have gone into developing wireless links to replace the miles of field cable, and hence improve its usability in mobile operations.  Work on radio link for sound ranging had started in the early 1920's.  However, while Bragg was undoubtedly on the right track, the challenges were significant, wireless technology was advancing quite quickly, but in the 1930's field sets were still quite large and had limited performance.  However, in 1938-9 further work occurred based on the No 11 wireless, an HF set.   A new version, No  11SR, was developed with a companion 'Sender SR No 1' connected between the microphone and the wireless, the pair being used at each microphone on its own frequency, and with an operator.  Co-located with the sound ranging recorder was the 'Receiver SR No 105'', this included a stack of five receiver modules, allowing the use of five microphones.   The equipment entered service in late 1940.

Radio eliminated the need for line maintenance and the vulnerability of line being broken by vehicles or cut by hostile fire, but had manpower implications.  Each microphone needed operators, primarily to switch on when the Advanced Post reported gun firing, but also to change batteries and keep the sets accurately tuned because they ‘drifted’off frequency so needed frequent re-tuning.  Finally, the time taken to accurately survey a SR microphone base was probably not much different to the time taken to lay line, so probably little difference in deployment time.  There was no quick and accurate survey solution on the horizon, it was five decades away.

The Manual of Sound Ranging was published in 1937.  It detailed all the approved practices including a choice of plotting methods.  This seems to have been the first War Office approved publication on all technical aspects of sound ranging.

Flash Spotting

The WW1 flash spotting instruments also remained in use.  The WW1 Flash & Buzzer board remained the only means for synchronising observations until about 1938 or 39 when a new procedure was introduced.  This enabled wireless reporting of flashes and hence did not require it, and the method enabled all posts and the plotting centre to be on a common wireless frequency.   In this procedure one FS post was designated 'Main' and controlled the spotting, the other posts being designated 'Sub-posts'.  Main reported 'Flash' to the Sub-posts whenever an HB flash was spotted.  Once at least two Sub-posts we observing the same series of flashes, all the posts reported their bearings to the Plotting Centre. The bearings were plotted on the Concentration Board with an arc for each OP and strings for plotting.  However, it appears that units retained the old Flash & Buzzer boards for use with line.  The first Manual of Flash Spotting was also published in 1937. 

However, in the 1930's Flash-Spotting Instrument No 4 Mk 1 appeared.  It’s not clear what Nos 1 – 3 were, but presumably retrospective numbering of the WW1 instruments and there are indications that at least some of these remained in use.  The No 4 was a binocular instrument with x9 magnification, a choice of 5 and 40 minutes Field of View and lighting to illuminate its graticules.  Bearings could be read to 2 minutes precision.  The new No 7 Director was also issued and the WW1 French Longue-vue monoculaire with its three magnifications was retained and referred to as the Telescope, but doesn’t seem to have been given an instrument number.  It was used by the Main FS post. 

The modified WW1 telephone Type D Mk III remained in use in the interwar period.  In seems to have been replaced around the time WW2 started.  However, standard plotting boards for flash spotting were introduced in the 1930's.  They appear to have been  'covers' of linen reinforced paper for the standard tripod mounted Artillery Board.  There were three types of cover for flash spotting.  One, the concentration board, was a plain grid used with pre-printed coloured arcs for flash spotting plotting (each post being given a different colour), it was used to plot the bearings reported by the posts.  The second (Parallel Ruler Board), was gridded with a printed full circle protractor in the middle, once a possible location was found using the concentration board the bearings were accurately plotted using a Parallel Ruler.  The third, the Large Scale Plotter was used for high precision plotting.


The Bristol F.2.B. remained the aircraft for army co-operation until about 1927.  It was successively replaced by the Armstrong-Whitworth Atlas (1927-35), Hawker Audax, and Hawker Hector, all bi-planes.  These larger, more powerful aircraft needed larger airfields and these were increasingly remote from forward units.  This added to liaison difficulties and the provision of air photographs, which could only be distributed as hardcopy prints.  However, while squadrons fostered the use of large scale maps and low-level navigation there was a lack of army co-operation doctrine, and arrangements for tasking and control. 

A new aerial camera, F24, capable of vertical and oblique photography was issued from 1922 although older cameras also remained in use.  This camera was issued to Army Co-operation squadrons.  In 1923 the wireless was the R.45 receiver that provided air to ground telegraphy for Arty/R.  In 1937 Tac/R were provided with two way wireless telegraphy using the T.1090 and R.1094, due to be replaced by the TR.1091.  Radio telephony (R/T) had been promised for Arty/R but it was cancelled in 1938.  Ground marker panels remained in use, and with them the need for Arty/R aircraft to ‘visit’ the gun position to see the marker panels. 

However, squadrons participated in brigade and divisional training exercises, with detachments at RA practice camps, lectures and demonstrations to Staff College, etc.  Nevertheless, there was not much understanding of air-ground issues in the army and it was not exercised as much as it should have been. 

In 1934 the RAF had issued a requirement for a new army co-operation aircraft to replace the Hector.  The result was the Westland Lysander that first flew in 1936 and entered service in 1938.  It had several advanced features and could accommodate the pilot and one passenger, and could be fitted with vertical F.24 cameras.  It was designed for short takeoff and landing on rough fields but size (50 feet wingspan), height (15 feet) and weight (2.5 tons) made it very difficult to handle and conceal easily. 

1935 also saw the first flights of the Messerschmitt Bf109 (in May) and Hawker Hurricane (November) these new generation monoplane fighters were 50% faster than their predecessors.  The significance was that for the first time fighter aircraft dramatically out-performed the Arty/R aircraft.  Nevertheless the German temporal and functional equivalent of the Lysander, the Focke Wulf Fw189, was very similar in performance and larger, it served in role throughout the war, notably on the Eastern Front but also in other theatres including N Africa.

The prospect of Lysander performing the Arty/R and Tac/R roles over enemy territory was fast disappearing unless a satisfactory air situation was achieved.  In essence Lysander wasn’t suitable for basing at forward airstrips due to its size and ground handling requirements and was outperformed by the new generation of fighters.  The reliance of CB on air observation and photography over the enemy gun areas using the approved army co-operation aircraft was becoming difficult. 

In 1935 the RAF conducted trials of Cierva design Auto giro C30A, manufactured by AV Roe & Co, for the army co-operation role.  The trials included RA observation using normal artillery procedures and quick shooting, these were generally satisfactory.  One recommendation was that it should have an RA pilot who also observed.  Of course these light aircraft were unsuitable for flying over hostile territory, and hence unsuitable for CB activities.

The RA Flying Club had formed in 1934, and an Air Observation Post (AOP - different to Arty/R) concept developed using small and slow aircraft flying mostly low over friendly territory, looking 2 or 3 miles into enemy territory with the pilot observing obliquely.  It was easier to teach gunner officers to fly than for RAF pilots to learn gunnery.  However, while it had potential and demonstrated this from 1943 onwards, it was not really suitable as a key element in the CB battle because it couldn’t fly over the enemy gun areas.  Nevertheless the War Office put the case to Air Ministry in 1938, the RAF was not enthusiastic but joint trials by 22 Army Co-operation Group and the School of Artillery took place in early 1939 using Audax and Lysander – both proved unsuitable for the AOP role.  The Army wanted further trials tests of 3 or 4 types including autogiros, but the start of war prevented this.


The range of medium and heavy guns had increased significantly during WW1, and this continued immediately after the war with the introduction of streamlined shell shapes (the D series of shells) first used with 60-pr in the second half of 1918.

After WW1 it had been decided to keep 60-pr Gun, 6-inch Howitzer, 6-inch Gun and 8-inch Howitzer in service, with 9.2-inch Howitzer in store.  The latter was not forgotten because a new Handbook for the gun was published in 1931.  The guns in service were modified for vehicle towing, initially with solid rubber types, subsequently, in the 1930's, with pneumatic tyres and improved brakes suitable for faster towing speeds.  Sight mounts were changed to the Probert calibrating pattern.

In 1935 the Director of Artillery (a technical position responsible for equipment matters) identified the requirement to replace both 60-pr and 6-inch medium guns with a new equipment that would provide the mainstay of the CB effort among other tasks.  The initial proposal was to line down 60-pr Gun to 4.5-inch and develop a new ordnance for the 6-in Howitzer  The specification for the latter was 16,000 yards range, 85 lb HE shell, 3 charges and weighing 30 cwt, the latter was very optimistic for the technology of the time.  It led to 5.15-inch design with many problems.  In 1936 the requirement evolved to 5-inch gun/howitzer giving 18,000 yards range, 3 charges and a 78 lb HE shell – design work to continue.  In the meantime 60-pr(5-inch) was successfully lined down to 4.5-inch, giving 20,000 yards with a 55 lbs HE shell, a substantial improvement on the 60-pr’s 15,100 yards . 

The need to replace the 6-in How remained.  At the beginning 1939 the specification for 5.5-inch was published:16,000 yards range, 90-100 lb HE shell and an total weight of no more than 5.5 tons.  In the spring of 1939 the design for the 5.5-inch gun emerged and development started.   Building on this success the Director of Artillery decided to design a new 4.5-inch with a 55 lb shell.  Work started on a new split trail carriage for 4.5-inch and 5-inch with pneumatic tyres, 60 degrees of top traverse and weighing 5.5 tons.  

While medium artillery was the backbone of the CB effort, there was still the heavy artillery.  Designs for a new 8.8-inch How and 6-inch Gun had been consider in the mid 1920's.  In 1938 it was decided to develop a gun firing a 100 lb shell to 26,500 yards and a howitzer firing  a 300 lb shell to 16,000 yards, and in early 1939 a 7.85-inch howitzer and a 6.85-inch gun were decided on.  In late 1939 this changed to an upgraded (more mobile) 9.2-inch howitzer and the 6.85-inch gun abandoned.

At maximum range 60-pr had a 56 seconds time of flight and 12,500 feet vertex (trajectory height).  4.5 inch was to have a maximum range of 20,500 yards with 69 seconds time of flight and 19,000 feet vertex.  The problem was the meteor data that was essential for map shooting.  The process for calculating the ‘Correction of the Moment’, ie the correction for non-standard meteor conditions was sound.  Army Form B2551 was used to calculate the corrections for sets of three different ranges, with sets for various charges.  These corrections could then be interpolated or graphed to find the correction for a specific range.

The RAF was responsible for providing meteor data in the field but its field equipment was limited in its performance.  Wind data was captured by optically tracking a pilot balloon, entirely achievable providing the cloud-base was sufficiently high.  Other data notably virtual air temperature and barometric pressure were also required.  The only means of providing this were ground measurements adjusted for height using standard factors and data from synoptic forecasts.  Inevitably the accuracy of this data was imperfect and magnified by longer range guns and their higher vertex.  A low cloud-base could result in significant errors in the wind data. 

The final notable innovation was the development of triple-base propellant for guns.  One feature of this new propellant was a significant reduction in muzzleflash, which reduced the vulnerability to flash spotting. 


Broadly, the objective of CB was to neutralise hostile batteries, although destruction was considered possible with air observation.  CB fire could form a part of any commander’s fire plan.  It was to be conducted in accordance with a corps commander’s policy.  It depended on accurate and up to date information about hostile battery positions, which was not easy to acquire in mobile warfare.  Air photography together with SR and FS were the primary sources for target acquisition.

However, a major problem was emerging.  Arty/R from an Army Co-operation Lysander overflying hostile forces was not going to be easy after the change to high performance mono-wing fighters in the mid 1930's. 

An additional problem was accurate map shooting for CB fire from longer range guns with increasing gun to target range which magnified the errors in map shooting.  This data was derived from ground measurements and visually observed balloons for wind data.  Other data for non-standard conditions above ground was derived from standard tables which could be significantly different to actual conditions.  Ranging was only possible with SR or with flash spotters observing airbursts but the inaccuracy of powder burning airburst fuzes hindered accurate airburst ranging at long ranges. 

Against an enemy with a competent and powerful artillery arm the British Army could be in trouble.  Fortunately Germany did not have a large field artillery arm as it did in the previous war because Blitzkrieg relied on airpower for fire support.



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