As Greg enters his last week at Yatesbury, the first flight of the day saw some consolidation work on zone calls, and the second flight didn’t end well:
Log book entry
Date: 30.4.18
Hour: 8.15
Machine type and No.: BE2E 8660
Passenger: –
Time: 35 m
Height: 600
Course: Zone calls
Remarks: –
Date: 30.4.18
Hour: 11.30
Machine type and No.: BE2E 1358
Passenger: –
Time: 40 m
Height: 2000
Course: Aerodrome
Remarks: Practice Crashed on landing
This was the second day running of zone call work, as explained in yesterday’s post:
The question arises whether the crash on landing at the end of the second flight was deliberate, so as to practice what happens in the event of a crash. The absence of a full stop or other punctuation mark after ‘Practice’ leans in the direction of that interpretation. Leaning the opposite way, though, are (a) the capital C of ‘Crashed’, and the fact that the past participle (‘Crashed’) rather than the noun (‘Crash’) was used. For my money, the crash wasn’t deliberate – though no doubt useful practice!
No flying the following day. Greg’s next log book entry is for Thursday 2 May 1918.
Operation Georgette comes to a halt. Around Merville, though, where Greg would be operating, there had not in fact been much movement in the German advance for a couple of weeks.
On the Lys, German front line passed between Merville and St Venant, not far from the settlement of St Floris.
Header Image: Adapted from Map 7 of Haig’s Despatches ‘The German Offensive on the Lys, April 1918’. Credit: Imperial War Museum and Great War Digital
In an important training exercise, Greg begins today to practice ‘zone calls’.
Log book entry
Date: 29.4.18
Hour: 2.35
Machine type and No.: DH 5155
Passenger: –
Time: 55 m
Height: 3000
Course: Aerodrome
Remarks: Practice.
Date: 29.4.18
Hour: 5.55
Machine type and No.: DH 5155
Passenger: –
Time: 1 h 20 m
Height: 3000
Course: –
Remarks: Zone calls
Date: 29.4.18
Hour: 8.0
Machine type and No.: RE 5146
Passenger: –
Time: 30 m
Height: 2500
Course: Aerodrome
Remarks: Practice 1 landing.
Zone Calls
Zone calls are one way wireless messages by Morse code from aircraft to artillery batteries giving information about targets, such as enemy batteries firing, enemy transport and troop movements.
A zone call might be something like:
NF L 26 c 2 0
Example of a zone call, with map reference – somewhere in France. All will be revealed on 8 August (although there is enough information in this post to identify where…). Adapted from 1:10,000 scale trench map (credit: Great War Digital).
This would mean: Guns Now Firing from a position at map reference L 26 c 2 0. Maps of the Western Front (and presumably maps used by Greg’s Training Squadron at Yatesbury) 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.
Each 6,000 yd square was in turn 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 with the required degree of precision. 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), which would identify a 5 yd square within the 50 yd square denoted by 2 0.
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, which were revised 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.
If this combination of squares and grid references sounds complicated, it is not actually different in principle from an Ordnance Survey grid reference, which in one of its incarnations 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 – which, as it happens, is on the former Yatesbury airfield (1:50,000 Landranger sheet 173 in today’s OS maps).
A zone call was a one way wireless message from the aircraft to an artillery battery on the ground. Ground to air communication was done by ‘ground strips’, as explained in this earlier post:
Only one flight today after yesterday’s four, but still practising landings:
Log book entry
Date: 27.4.18
Hour: 5.30
Machine type and No.: RE 6647
Passenger: –
Time: 55 m
Height: 3000
Course: [Aerodrome]
Remarks: Landings 4.
You can’t really over-practice landings. After all, in aviation it was as true in 1918 as it is today that although takeoffs are optional, landings are mandatory.
42 Squadron RAF, Greg’s future squadron, moves the 4½ miles (7 km) southwest from Trèzennes (aka Trezennes or Triezennes), just outside Aire-sur-la-Lys to Rely, Pas-de-Calais, on top of the low chalk hills to the southwest.
42 Squadron’s move WNW from Trèzennes to Rely, Pas-de-Calais, shown on a modern map (courtesy Google). Click for a larger, zoomable map (opens in new tab)
It was no doubt the continuing westward advance of German forces in Operation Georgette that occasioned the move to Rely, although by 25 April 1918 the line had practically been held some 6½ miles (10½ km) to the east of Trèzennes. For more on Georgette and the Spring Offensives in General, see:
Three flights today: the first in an RE8 around the aerodrome – with an intriguing entry (‘Vacuum Control’) in the Remarks column – and two further afield flying in formation and on a compass course.
Log book entry
Date: 25.4.18
Hour: 2.50
Instructor: –
Machine type and No.: RE 6647
Passenger: –
Time: 45 m
Height: 4500
Course: Aerodrome
Remarks: Vacuum control
Date: 25.4.18
Hour: 5.55
Instructor: –
Machine type and No.: DH6 7670
Passenger: –
Time: 55 m
Height: 2000
Course: Marlboro. Swindon. Aerod.
Remarks: Formation
Date: 25.4.18
Hour: 1.10
Instructor: Lt Gowler
Machine type and No.: RE 3551
Passenger: –
Time: 50 m
Height: 2000
Course: Compass course (Wootton Basset, Chippenham &
Devizes. 5 forced landings)
Remarks: DUAL
Vacuum Control
So what was the ‘vacuum control’ of the first entry (but not the first flight) of the day? I’m grateful to Duncan Curtis, who has provided this authoritative explanation:
‘Vacuum Control’ relates to a feature on some aircraft/engines, whereby the carburettor/s were equipped with vacuum controls. The vacuum control feature allows the pilot to adjust engine mixture for altitude: on early engines no adjustment; then on some engines manual adjustment; and finally all engines gained automatic adjustment via vacuum bellows (post-WW1). For service types equipped with these engines (of which the RE8 was one), the pilot had to demonstrate correct operation prior to graduating ‘B’ on his operational type.
Requirements to graduate ‘B’ (from Higher Instruction), referring to Vacuum Control in point 8. Click for larger image. Credit: Duncan CurtisA page from the RE8 parts catalogue showing that Claudel and BB carburettors were fitted with vacuum control. Click for larger image. Credit: Duncan Curtis
[Topic updated 25 September 2018]
Formation Flying
The second aerial event of the day was some formation flying on a circuit from Yatesbury to Marlborough to Swindon and back, a distance of some 30 miles (48 km):
Yatesbury-Marlborough-Swindon flight shown on a modern map (courtesy Google). Click for a larger, zoomable map (opens in new tab)
Cross Country
The third entry in the log book, but actually the first flight of the day, was a cross-country compass course under dual control with Lt Gowler as instructor. The course was a 34 miles (54 km) circuit from Yatesbury to Wootton Basset to Chippenham to Devizes and back.
Yatesbury-Wootton Bassett-Chippenham-Devizes cross country route shown on a modern map (courtesy Google). Click for a larger, zoomable map (opens in new tab)
In a remarkable military achievement on Anzac Day 1918, British and, particularly, Australian forces retook Villers-Bretonneux from German forces who had taken the town the previous day, in the Second Battle of Villers-Brettoneux.
Although this action was in the Somme sector before Greg arrived in France, an oblique aerial photograph of Villers-Bretonneux found its way into his collection. It’s being published today on Anzac Day in honour of the events 100 years ago:
Oblique aerial view of Villers-Brettoneux from the North East. Click or tap for larger image (opens in new tab). Image credit: Greg’s War Collection.
For comparison, here is a broadly similar, contemporary view generated from Google Maps:
Villers-Brettoneux on Google Maps. Click or tap for larger image (opens in new tab)
For more about the Second Battle of Villers-Brettoneux on 24 and 25 April 1918, see the new ‘Setting the Scene’ article:
A day of varied activity, and varying degrees of success. First some aerial combat practice in a DH.6. Secondly an outing in an RE8 to take photos and do a shoot – presumably an artillery shoot, as on 22 April – which this time was recorded as unsuccessful.
Log book entry
Date: 24.4.18
Hour: 2.25
Instructor: –
Machine type and No.: DH6 9762
Passenger: –
Time: 45 m
Height: 1500
Course: Aerodrome
Remarks: Fighting
Date: 24.4.18
Hour: 4.40
Instructor: –
Machine type and No.: RE 5146
Passenger: –
Time: 1 hr 0
Height: 2000
Course: Photos & shoot
Remarks: Unsucc.
Operation Georgette comes to a halt. Around Merville, though, where Greg would be operating, there had not in fact been much movement in the German advance for a couple of weeks. 
