Counter Battery Patrols and Zone Calls

Greg devoted much of his time on the Western Front to ‘Counter Battery Patrols’, often abbreviated to CBPs and otherwise known as Artillery Patrols.  Counter Battery Patrols/Artillery Patrols were one of the principal activities of the ‘corps’ squadrons such as 42 Squadron. They were also one of the most important ways in which the artillery could acquire targets  So CBPs were frequent patrols on the lookout for hostile batteries. These batteries might be detected by direct observation of the guns. More likely, tell-tale puffs or flashes would reveal their location when they were fired.  The aircraft would relay the position of the guns to the artillery, who would note them on a map.  All this was to prepare for counter-measures to be taken at the appropriate time.

Location of Hostile Batteries by Counter Battery Patrols/Artillery Patrols

The booklet ‘Co-operation of Aircraft with Artillery‘ [SS 131], issued by the General Staff in December 1917 explains the overall nature of the counter battery patrol:

10. Location of Hostile Batteries. – At least one machine should be up in every corps counter-battery area during the hours of daylight, whenever flying is possible, as an artillery patrol to locate targets.

Even when low flying only is possible much useful work can be done by artillery patrols working from behind their own troops, especially in spotting flashes, which are more easily seen on a dull day, and in reconnaissance of the enemy’s trenches.

The duties of an artillery patrol are:-

(i.) To locate new hostile batteries, and report those seen to be active.

(ii.) To reconnoitre all known hostile battery positions, especially those only roughly located or reported from other sources, and to fix their exact positions if possible.

(iii.) To observe fire, if so ordered, on hostile batteries seen active. [Elsewhere it is cautioned that information secured by reconnaissance may be of greater value to the corps than stopping the fire of a single hostile battery.]

(iv.) To locate new trenches, machine gun emplacements, and hostile works generally.

(v.) To record any movement seen and to report it to the artillery, if within range.

Counter battery patrols were self-evidently concerned with duties (i.) and (ii.) in particular.

Communication in Counter Battery Patrols – Zone Calls

The aircraft were generally equipped with one way (air-to-ground) radio.  Zone calls are one way wireless messages by Morse code from aircraft giving information to the artillery about targets, such as enemy batteries firing, enemy transport and troop movements. (Ground-to air communication from the artillery was generally by means of cloth strips.)

A zone call might be something like:

LC NF L 26 c 2 0

Zone call map
Example of a zone call, with map reference – somewhere in France.  Adapted from 1:10,000 scale trench map (credit: Great War Digital).

This would mean:  in map zone LC, guns are Now Firing from a position at map reference L 26 c 2 0. Maps of the Western Front used a reference system that was a combination of squares and a grid. 

  • Each 1:40,000 map sheet was divided into twenty-four 6,000 yd squares, arranged in a 6 x 4 array and lettered A to X – in our case, L
  • Every 6,000 yd square was quartered into four 3,000 yd square zones -here LALBLC and LD, and the zone with which we are concerned is LC.  (There’s a more detailed explanation of zones below, under ‘Hostile Battery Numbers and Zones’)
  • Every 6,000 yd square was also subdivided into thirty-six 1,000 yd squares, numbered 1 to 36 – in our case, 26.
  • Each 1,000 yd square was then subdivided into four quadrants (a, b, c, d) – in our case, c.  
  • Finally, a decimal grid reference (eastings and then northings) was used to specify the intended position. This could be to one significant figure as in our example (2 0), which identified a 50 yd square.  Or it could be to two significant figures if greater precision was desired and achievable (22 01, for example). This would identify a 5 yd square within the 50 yd square denoted by 2 0.

There is an element of duplication in the resulting zone call LC NF L 26 c 2 0, in that the letter L appears twice.  Zone LC was necessarily within square L and so was strictly not needed. But the call began with the zone identifier since aircraft were allocated to watch particular zones, and all parties knew immediately in rough terms the area to which the rest of the message would relate.

Different Map Scales

Fine levels of detail are not visualisable on a 1:40,000 map.  The artillery and infantry tended to use 1:20,000 and 1:10,000 scale maps, depending on the purpose in hand. Surveyors revised these maps periodically as trenches and other ground features changed.  These revisions, incidentally, would rely heavily on the aerial photography of work of the corps squadrons.  The complete map reference would include the number of the 1:40,000 sheet (eg Sheet 36A, to give 36A  L 26 c 2 0), but the sheet number was typically understood in context and therefore omitted in zone calls.

Similarity to OS Grid References

If this combination of squares and grid references sounds complicated, it is not actually different in principle from an Ordnance Survey grid reference.   In one of its incarnations, the OS grid reference  uses a combination of an identified square and a decimal grid reference within the square.  For example, the OS reference SU 053711 is based on a 100 km square designated SU and then, within that square, a three significant figure decimal grid reference 053 711. This in turn identifies a 100 m square.  As it happens, the example reference is on the former Yatesbury airfield (1:50,000 Landranger sheet 173 in today’s OS maps).

Hostile Battery Numbers and Zones

Once a hostile battery has been identified, it is given a short alphanumerical zone reference.  This is easier to use than the full map reference.  For this purpose, the lettered map squares A-X of a 1:40,000 map sheet are divided into four 3,000 yard quadrants called zones.  Each of those quadrants contains nine of the numbered 1,000 yard squares used in the zone call above. (Occasionally there were exceptions to this.)  But to take a typical case, the 6,000 yard square Q of sheet 36A is quartered into zones QAQBQC and QD.  These zones would be made up of the following numbered 1,000 yard squares:

Then, within each of the 3,000 yard square zones QAQBQC and QD, hostile batteries or other features of interest are given a zone number.  How this zone number is assigned is explained below.  But for now we can take it that, for example, QB 23 refers to a hostile battery given number 23 within zone square QB.  That battery might first have been identified in an NF (Now Firing) zone call that gave its position as follows:

 QB NF Q 5 c 4 3.

But once identified at that position it was given a QB zone number, in this case 23, and marked on the map.  When the same battery was next observed to fire, the zone call would be the simpler:

QB NF 23.

This is how a marked 1:20,000 map looked.  The artillery tended to prefer this scale.

1:20,000 map of Sheet 36A Q
1:20,000 map of Sheet 36A Q, subdivided into four 3,000 yard zones QA, QB, QC and QD. Annotations show hostile batteries and other features identified by counter battery patrols and other means. Map credit: IWM/TNA/GreatWarDigital

Assigning a Zone Number to the Target

The zone number, QB 23 in the above example, was assigned according to the following system.  In each zone (such as QB) there will be nine 1,000 yard squares. On the maps, these 1,000 yard squares will originally be numbered according to their position within the 6,000 yard square (here Q).  For a ‘B’ zone such as QB, the nine 1,000 yard squares will be 4, 5, 6, 10, 11, 12, 16, 17 and 18 – see the grid diagram above.  

But for the purpose of assigning the zone number of an object of interest, the nine 1,000 yard squares of the zone are notionally numbered 1 to 9, whatever their original numbers. For a ‘B’ zone, original square 5 becomes numbered 2, as it is the second square in the zone. This number gives us the first digit of the zone serial number.   The second digit is assigned in sequence, starting with zero.  So the first object of interest to be located in what was originally 1,000 yard square 5 of 6,000 yard square Q is designated QB 20.  And we can tell that QB 23 designates the fourth object of interest to be located within that square.

A Slight Complication

A minor extra complexity to this is that, to avoid confusion between the quadrants of the 6,000 yard squares (e.g. the Q square) of adjacent 1:40,000 maps running along the front, the quadrants of the 6,000 yard squares of the adjoining sheets would be lettered with W, X, Y or Z, as in  QWQXQY and QZ, rather than A, B, C or D.  This would apply to the sheet to the north of sheet 36A (sheet 27) and the sheet to the south (sheet 36B). The sheets would then alternate with the ABCD series and the WXYZ series along the line of the front.

A More Detailed Look at a Counter Battery Patrol/Artillery Patrol

Greg’s counter battery patrol on 3 July 1918 was the first for which not only Greg’s log book and diary are available but also for which we have the official report in 42 Squadron’s Record Book.  So here is a more detailed look at what Greg saw and did on patrol that morning.  He was sending signals of features of interest every five or ten minutes. The Squadron Record Book entry is hard to read, so a transcription is given, along with some interpretative notes.

Squadron Record Book

42 Squadron Record Book entry for 3 July 1918.
42 Squadron Record Book entry for 3 July 1918. Click for larger image.
Type and Number: R.E.8.27

Pilot and Observer: P. Lt Gregory. O. Lt Pring.

Duty: Artillery Patrol

Hour of Start: 6.20am

Hour of Return: 8.40am

Remarks: 
6.30am E.K.B. S of ESTAIRES.  6.40am sent 2 R.E.A. K.D. 6.55am sent K.D. N.F. K.30.b.2.4. Battery silenced.  7.10am sent 3 S.E.A. L.C.  7.15am fire Q.4.c.5.5.  7.20am 2E.K.B. S. of ESTAIRES. 7.30am C.W.S. sent Q.B.  No flashes observed Q.B.  7.35am 2E.K.B. E. of ESTAIRES.  7.40am fire at K.24.c.4.3.  7.45am fire Q.36.a.8.2.  7.50am 3 E.K.B. N. of ESTAIRES.  8.5am C.W.S. sent Q.B.  No flashes seen in Q.B.  Obs. Fired 100 rounds into MERVILLE.  Pilot 200 rounds into buildings in Q.B.  A.A. normal.  E.A. active. Vis. poor very cloudy.  Obs by P. & O.

Translation of Remarks

The map extract below shows the zones and map references mentioned in these interpretative notes.

Remarks: 
6.30am E.K.B. S of ESTAIRES.  [Enemy kite balloon south of Estaires]

6.40am sent 2 R.E.A. K.D. [Two reconnaissance enemy aircraft in zone KD (Merville)]

6.55am sent K.D. N.F. K.30.b.2.4. Battery silenced.  [Signalled: in zone KD (Merville), enemy guns are now firing at map reference K.30.b.2.4 (east of the town centre).  That 'zone call' elicited a response (from the British artillery, probably) that silenced the enemy guns.]

7.10am sent 3 S.E.A. L.C.  [Three scout (fighter) enemy aircraft seen in zone LC, which is east of Merville]

7.15am fire Q.4.c.5.5.  [There is a fire burning at map reference Q.4.c.5.5, which is southwest of Merville]

7.20am 2 E.K.B. S. of ESTAIRES. [Two enemy kite balloons south of Estaires]

7.30am C.W.S. sent Q.B.  No flashes observed Q.B. [Central Wireless Station requested aircraft to investigate zone QB, south of Merville, but no flashes (which would indicate guns firing) were seen.]
  
7.35am 2 E.K.B. E. of ESTAIRES.  [Two enemy kite balloons east of Estaires]

7.40am fire at K.24.c.4.3.  [There is a fire burning at map reference K.24.c.4.3, northeast of Merville]

7.45am fire Q.36.a.8.2.  [There is a fire burning at map reference Q.36.a.8.2, south of Merville]

7.50am 3 E.K.B. N. of ESTAIRES.  Two enemy kite balloons north of Estaires]

8.5am C.W.S. sent Q.B.  No flashes seen in Q.B.  [Central Wireless Station again requested aircraft to investigate zone QB (south of Merville), but no flashes (which would indicate guns firing) were seen.]

Obs. Fired 100 rounds into MERVILLE.  
Pilot 200 rounds into buildings in Q.B. [south of Merville].  
A.A. [anti-aircraft fire] normal.  
E.A. [enemy aircraft] active. 
Vis. [visibility] poor very cloudy.  
Obs by P. & O.

Map Extract Showing Principal Zones and References in Squadron Record Book Entry

Merville and surrounding area
Merville and surrounding area, showing zones and map references referred to in Squadron Record Book entry. Map credit: IWM/TNA/GreatWarDigital

There are more details of Greg’s activities on 3 July 1918, in addition to his counter battery patrol, here:

Wednesday 3 July 1918 – CBP and a Practical Joke

In Conclusion…

Counter battery patrols, or artillery patrols, were frequent patrols to identify hitherto unknown or newly active enemy batteries or other features of interest. Wireless messages identifying or reporting on such targets were known as zone calls. Newly identified batteries would be added as new features (QB 23LX 76 or KD 90, say) to maps such as those described above.  Artillery commanders could then schedule appropriate counter-measures.  Of course,this was in competition with all the other priorities that they had to worry about.

 
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