One of the things I love about the official history of the RFC and RAF in the First World War is all the maps -- multi-panel fold-out jobs showing where bombs fell in London during the Gotha raids, or the Allied front in Macedonia. That's not to mention the accompanying slip-cases stuffed full of more maps of the paths taken by Zeppelin raiders and the like. I could pore over these for hours ...

Here are a couple of the maps (or parts thereof) showing two different kinds of barrages associated with the air defence of Britain.

The first one is entitled 'Aeroplane barrage line. December, 1916.' It's too big to show effectively, so I've just reproduced a portion showing the coast of Lincolnshire and Yorkshire. The red squares show home defence squadron HQs: 33 Squadron at Gainsborough and 76 Squadron at Ripon. The red triangles are flight stations, the red stars flight stations with searchlights, the blue circles are searchlight stations under squadron control ('aeroplane lights') and the black circles are warning control centres (Hull).

As I've discussed before, artillery barrages weren't the only kinds of barrages. Originally they seem to have just been barriers or walls of some kind (barrage originally referred to a dam). Here the barrage is composed of aeroplanes and searchlights, a wall erected to hopefully bar Zeppelins coming in over the North Sea from reaching the industrial cities behind the line. And it does look like a barrier: on the full map it stretches from Suttons Farm (later renamed Hornchurch) near London all the way up to Innerwick, east of Edinburgh (with extensions in Norfolk and Kent). But it's not a physical barrage, for the most part -- it's aerodromes and searchlights. Previously, home defence squadrons had been placed close to target areas, because of doubts about night navigation and interception. Experience had shown that these problems weren't as great as previously thought:

Now that it was clear the aeroplane patrols could be extended, it was suggested that the Flights situated near Birmingham, Sheffield and Leeds should be moved farther east as a step towards the ultimate establishment of a barrage-line of aeroplanes and searchlights parallel with the east coast of England.¹

This system worked very well against Zeppelins (as one indication, note the steep drop in casualties due to airship raids from 1917 on). But not so well against Gothas.

This map shows the anti-aircraft gun barrage in and around London in October (or so) 1917, which were there to defend against night raiders -- aeroplanes, now, much more than airships. Not that the guns were particularly effective, but they were heavily used. So heavily used, in fact, that there was a serious concern that London would soon run out of AA guns through wear and tear (each gun lasted for a maximum of 1500 rounds, and 14000 rounds total were fired on 30 September alone).²

But the barrages on this map, the red lines, do not show the location of the guns. They show lines in the sky along which a number of guns could be brought to bear (which explains why they are mostly made of arcs). So, again, the barrages are barriers. As the note in the top left corner explains:

Note. This type of barrage, usually known as 'Linear', allotted fuzes, bearings, and quadrant elevations so that fire could be directed at a particular altitude over a definite area. The barrages varied in length and form according to the situation and number of the guns which could be brought to bear. The height of the barrage could be varied at will. Orders for this form of barrage were given only occasionally, usually to 'screen' certain important objectives or to catch raiding aeroplanes whose courses were doubtful.

So, if I understand this correctly, if Gothas were seen approaching Woolwich Arsenal from the south-east, several guns would receive the order 'Ace of Spades' and would then swing to pre-determined settings to set up a barrier of fire for the raiders to fly into. If they flew on instead towards the Isle of Dogs, the order 'Robin Hood' would then be sent, and a new barrier would be set up, probably drawing on some of the same guns but with others joining in too.

There were also guns arrayed along the grid squares, the original scheme to which the linear barrages were a supplement. There is a hint that the linear barrages were meant to be a more efficient, more selective alternative, to help with the wear and tear problem.

As an aside, I wonder who came up with the barrage names? Some of them could be standard military issue: Kingfisher, Mercury, Union Jack. But what about Noisy Norah, Charley's Aunt or Dandy Dick? (The last two, at least, seem to be the names of popular farces.) Did the gun crews have a say in it, or were they named on the whim of some bored junior officer?

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1. H. A. Jones, The War in the Air: Being the Story of the Part Played in the Great War by the Royal Air Force, volume 3 (Oxford: Clarendon Press, 1931), 166. The map faces 170. [↩]
2. H. A. Jones, The War in the Air: Being the Story of the Part Played in the Great War by the Royal Air Force, volume 5 (Oxford: Clarendon Press, 1935), 85-6. The map faces 89. [↩]