Some more plots from the talk I gave the other way. I was trying to think of a way to illustrate in concrete terms the problem of speed for the air defence of Britain. I came up with the following:

Simply put, it shows the length of time it would have taken for an attacking bomber to fly from the coast to London (in blue) — call it the crossing time — and the time it would take taken for a defending fighter to climb high enough to intercept (in red) — call it the intercept time. And how these changed over time, obviously. As can be seen, the fighters generally had enough time to climb high enough to intercept the bombers before they got to London, but the margin decreased over time, from 15 or so minutes during the First World War, to less than 5 in the Second.

But all this is not straightforward so I’ll explain further. To begin with, the data is slightly dodgy. It’s mostly drawn from the same source as this, which is fine as far as it goes. But that means that I’m showing how long it would have taken British bombers to penetrate from the coast to London, which was not really a great worry. Having said that, it’s probably reasonable to assume that the performance of British bombers was roughly in line with those used by Continental air forces. (And the RAF’s own air defence exercises had to make this assumption, too, because borrowing somebody else’s air force for a day wasn’t feasible.) One day I’ll create a dataset for European aircraft …

How are the numbers derived? First, the bombers (blue). This is just the distance from the coast to London divided by each bomber’s maximum speed (which is not necessarily realistic). Why the coast? Because it was only when the incoming raiders crossed the coast that they could be detected by ground observers, and fighters dispatched to intercept them.¹ What is the distance from the coast to London? Well, obviously it varies, depending on which direction the enemy came from (and some writers expressed fears that they would fly up the Thames Estuary and avoid detection). Looking at a map, 50 miles seems like a reasonable approximation.

Next, the fighters (red). The time it takes for a fighter to climb meet the bombers is the height of the raid divided by the climb rate of each fighter. This climb rate is a bit of a problem. I don’t a good source for this number and had to plunder Wikipedia. That’s bad enough in itself, but it’s worse because the data is inconsistent. Sometimes — when it’s not missing — it’s expressed in feet per minute, and sometimes in the number of minutes to reach a given height. Obviously one can be turned into the other, but actually both are only approximations, and I’ve had to extrapolate and interpolate from these to get a usable number.² What height would the bombers be at? Well, that varied — it was higher on average during the Second World War than in the First because aircraft were more capable, and also because bombers tried to climb higher to escape the fighters. I’ve assumed that this height was 10000 ft in the 1910s, 15000 ft in the 1920s, 20000 ft in the 1930s, and 25000 ft in the 1940s.³ I just plucked these numbers out of the air, more or less, but they seem to work well in terms of keeping the red and blue trends in touch with each other. If anything they are probably underestimates.

Some other points. Firstly, the fighters would generally have to move horizontally to intercept the bombers, as well as vertically. This plot says nothing about that. But given the edge fighters had in speed and the location of their aerodromes, they should be able to cover that distance while climbing. Secondly, the data points are for the year each aircraft entered into RAF service. But since they remained in service for several year, at least, the data points should really be horizontal lines.⁴

Thirdly, I’m assuming a perfect command, control, communications and intelligence system. Fighter Command (and its predecessors) was good, but it still took a finite but non-zero amount of time for sightings to be reported, sifted, collated and reported, and then for squadrons to be allocated, given orders, and take off. Also there was a chance that raids might not be observed, that squadrons could be given the wrong vector, that the enemy could be missed in cloud — so the greater the gap between the red data points and the blue ones the better. The more inefficient Fighter Command, the narrower the margin for error.⁵

Now we can show what difference radar made. The Chain Home system came into operation in 1939 and had an effective range of 120 miles. What this means here is that instead of only having to cross 50 miles from the coast to London after being detected by the observers on the coast, the bombers now had to cross 170 miles after being detected. As the above plot shows, this pushed up the crossing time dramatically: from 1939, the defenders could generally expect to have around 40 minutes’ warning of any raids. The margin for error increased dramatically, from only 5 minutes or less, to more than half an hour, which is far better. In theory, the defending fighter squadrons would now have plenty of time to get in position before the enemy arrived. Of course, that’s not the whole battle, but it’s a good start!

Lastly, here’s a counterfactual which I’ve long wondered about. Between 1933 and 1935, the Air Ministry put a fair amount of effort into researching the feasibility of using acoustic mirrors as a comprehensive early warning system. The acoustic mirrors were, mostly, concrete hemispheric dishes for focusing sound, which had been used as early as 1916. The biggest ones, at Dungeness in Kent and Maghtab in Malta, were 200 feet long curved walls. Land was actually purchased along the Thames Estuary for the beginnings of a national acoustic mirror system, but work never started because radar came along. But if it hadn’t, then in 1940 Fighter Command might have relied upon a network of these acoustic mirrors all along the coast.⁶ How useful would they have been?

The experimental mirrors had a maximum detection range of 22 miles (on very windy days it was a lot less). I’ll be generous and call it 25 miles, which is then added to the 50 miles from the coast to London for a total distance of 75 miles. The Thames Estuary acoustic mirrors probably would have come online in 1936, and so again I’ll be generous, and assume that London at least would have a working early warning system from that year.

Taking all this into account, the results can be seen above. And sadly the acoustic mirrors wouldn’t have made much difference — a margin of only about 10 minutes, not much improved on the 5 minutes with no warning system. Of course, even a few minutes’ extra warning was worth having, but the Air Ministry was right to terminate development of the acoustic mirror network in order to concentrate on the far more promising radar.

John Ferris has argued against the idea that ‘Air defence in Britain began during 1934 and only because radar was developed’, and that the importance of the C³I system — ultimately a legacy of the First World War — has been underestimated by historians: it was ‘ideally preadapted to radar’.⁷ And he’s right. Even without effective early warning, as long as the enemy bombers could be intercepted and shot down on their way back home, air defence could still work by inflicting prohibitive casualties. Except, that is, when the casualties from bombing were predicted to be massive, and then a failure to stop the bomber getting through would have devastating consequences. Radar was part of the antidote to the fear of the knock-out blow. Or rather it could have been, if it hadn’t remained secret until 1941 …

(Just to repeat: the data and assumptions underlying these plots are on the dubious side, and are not fit for any purpose, probably including this one!)

1. I’m neglecting radar, obviously, but see below. I’m also neglecting the fact that sound detectors, of the type that had been developed during the First World War, had a range of about 5 miles. But see even further below. Distant patrol aircraft were also used as a kind of picket line.
2. What I really need are curves showing climbing time vs. height because the higher an aeroplane flies, the harder it is to climb in the thin air. I assume these are available somewhere, but digging them up is too much work for a quick and dirty plot like this!
3. Fighters got a lot better at climbing very rapidly by the late 1940s, but as that happens I’m shifting the goalposts ever higher, as it were, and so the above graph is understating the rate of climb of fighters.
4. E.g., the two red triangles in the late 1930s are the Hurricane and Spitfire, which between them were the RAF’s primary interceptors throughout the war. This plot makes it look like there wasn’t anything able to catch raiders in 1940, which was not the case!
5. I could model this inefficiency by adding a fixed number of minutes to the climb time of the fighters — call it the response time — but I don’t know what a reasonable number is and it might vary a fair bit. For instance, in 1918 LADA (London Air Defence Area) had a response time of 2.5 to 5 minutes, according to John Ferris, “Fighter defence before Fighter Command: the rise of strategic air defence in Great Britain, 1917-1934”, Journal of Military History 63 (1999), 853 (JSTOR). But it presumably rose after LADA was dismantled after the war. David Zimmerman, Britain’s Shield: Radar and the Defeat of the Luftwaffe (Stroud: Sutton, 2001), 25, seems to suggest that 5 minutes was the time it took in 1933 just to transmit observations to ADGB (Air Defence of Great Britain) HQ, but that’s for the big acoustic mirrors which probably required more computation than normal acoustic detectors. So, pending more comprehensive figures, I’ll just leave the response time out of it.
6. See ibid., chapter 2, for more on the acoustic mirror research of the 1930s.
7. Ferris, ibid., 845, 884.

The talk at Earth Sciences went well, I think. It was a good-sized audience and they seemed interested in what I had to say, judging by the questions afterwards. I also found out that one of the honorary fellows had actually lived in London during the war, and though only a child could remember watching out for V1s passing overhead and even the ‘electric’ atmosphere of the day that war was declared.

I was all set to record the talk, but forgot to fire up the audio app. At some point, I may try recording it again at home or just putting the text up. Until then, here are a couple of the graphs I used, along with some different ways of presenting the same numbers. (Except where indicated, the data is courtesy of Dan Todman, who compiled it from Home Office files. Thanks Dan!)

Firstly, this shows the civilian casualties (killed and seriously wounded) each month in Britain due to enemy action between 1939-1945. Most — all? — of these will have the result of bombing, so I’ve labeled it accordingly. (This is the counterpart of a histogram I did for 1914-1918, except that combined civilian and military casualties, and separated different forms of attack.) It’s easy to pick out the Luftwaffe’s major offensives: the biggest peak is September 1940, when the Blitz started; it ended in May 1941, after which casualties were never so high again. There’s a relative lull in January and February 1941, due largely to bad weather conditions. In April-June 1942, there’s the Baedeker Blitz and from January 1944, the Baby Blitz. Then there’s the V-1 offensive in June-September 1944 and the V-2 offensive in September 1944-March 1945.

I thought it might be instructive to compare what actually happened with what was predicted would happen: if the knock-out blow had attempted and if pre-war estimates of German airpower had been correct. I derived this from figures provided by Richard M. Titmuss, Problems of Social Policy (London: H.M.S.O., 1950), 9 and 12-3, which were estimates made circa 1938 by government bodies for a war starting in 1939. These lead to the following assumptions:

1. the Luftwaffe could deliver 3500 tons of bombs on London in the first 24 hours of an attack, and an average of 700 tons per day for some weeks thereafter (Committee of Imperial Defence)
2. the casualties caused per ton of bombs dropped would be 48 (24 killed, 24 seriously wounded) (ARP Department, Home Office)
3. the war would last for 60 days (CID)

It’s then simple to calculate that if a German knock-out blow launched on 3 September 1939 would have led to a bit over 1.1 million casualties in September and a bit over a million in October, 168000 on the first day of war. More than a million fatalities in just two months.

It’s easy to quibble with these assumptions — for example, I’m using the most pessimistic multiplier for casualties, but that’s partly because it’s easy to relate it to the definition of casualties I’m already using. And my assumption that the 700 tons per day could be kept up for 60 days may well be too high, but I can’t find anything better. The CID did estimate in 1937 that an aerial war of this length would kill 600,000 and wound 1.2 million, so that shows that I’m in the right range and also that officials did make these sorts of calculations at the time.

Anyway, the point of the histogram is to show that the actual bombing, as bad as it was, was nothing like as terrible as ‘the expected holocaust’ (as Tom Harrison termed it), and I think it succeeds — you can just make out the Blitz and the V-1 attacks, but they’re just tiny blips. However, precisely because of the huge disparity in scale, it’s hard to make a meaningful comparison.

In his graphs of all British casualties, Dan opted for running cumulative figures rather than monthly ones, and that is indeed better for showing the overall picture — whereas monthly is better at showing intensity, I think. So, here’s my actual vs. predicted plot redone in cumulative fashion. Even by the end of five and a half years of total war, the scale of the knock-out blow isn’t even approached. (In fact, I think that even when military casualties are taken into account, the knock-out blow still wins handily.)

Here’s a different way to present the monthly data. This time I’ve plotted the casualties on a log scale. This is good for showing changes in the order of magnitude, and it’s immediately apparent that the knock-out blow was around two orders of magnitude (i.e., about 100 times) more intense than the worst month of the Blitz.

Finally, the cumulative casualty figures on a log scale. So, overall, the civilian experience of bombing over the whole of the Second World War (mainly meaning the Blitz) was about one order of magnitude (i.e. about 10 times) less devastating than the knock-out blow predicted shortly before the war.

The knock-out blow would have been 100 times more intense and 10 times more devastating than the Blitz was — I’ll have to remember that!

A curious snippet from Margaret MacMillan’s account of the Paris Peace Conference, Peacemakers (2002):

Why not give it to Hughes of Australia, suggested Clemenceau.¹

The ‘it’ was Heligoland, a small island in the North Sea, off the north-western coast of Germany. For most of the 19th century it had belonged to Britain, which swapped it for Zanzibar to Germany in 1890 — when relations between the two countries were still friendly. But then the naval arms race started up, and Heligoland became a handy place from any attempt by the Royal Navy to approach the German coast could be interfered with. Which is why, in Paris in 1919, the question arose of what to do about it.

The Admiralty naturally wanted the island back, but presumed that the Americans would object. In the end, the compromise solution adopted was to destroy all of its fortifications. Presumably Clemenceau’s suggestion was that Australia, as a nation almost as far away from Heligoland as possible, be given a Mandate over Heligoland (to add to New Guinea and Nauru), so that neither Britain nor Germany would have control over the disputed territory. I don’t know how seriously he meant it, or whether it ever had a chance of getting up. But in my mind’s eye I could see Australia dominating the North Sea from its Heligoland base with our single battlecruiser … well, no. But what would have happened if Australia had been given a Mandate over Heligoland?

Well, for a start, I don’t think Australia would have been exactly regarded as a disinterested party by Germany: British Empire and all that. In practice, there probably wouldn’t have been much difference between Australia governing Heligoland and Britain governing it: precisely because we were so far away from Europe, we had nothing to gain from it and nothing to lose, except perhaps in terms of our international reputation. I don’t see any reason why we wouldn’t use it to benefit our friend (and protecting power), Britain, in whatever way they wished.

What use would it have been to Britain? MacMillan notes that the coming of the aeroplane was another reason why Heligoland seemed newly valuable. She doesn’t explain, but seems to imply that this is because of their potential use as airbases for offensive action. I doubt that it would have been of much use for Britain in this way — it was too small to have a really big airbase (only 1 sq. km!) to be very powerful, and too close to Germany (only 70 km away) to survive for long.

But what Heligoland might have been very useful for was as a RDF (radar) station, to give Britain early warning of an incoming knock-out blow. It was actually ideally placed for this purpose.

This map, taken from The Chosen Instrument (1938) by Norman Macmillan (no relation, as far as I’m aware), shows the ranges from the various ‘heavily-armed air powers’ (France, Germany, Italy) to Britain. I’ve marked the rough range of a hypothetical Chain Home RDF station on Heligoland in red: it covers the entire German north-west coastline very handily.² So, assuming the Luftwaffe respected Dutch neutrality, any bombers they sent to Britain would have to pass through Heligoland’s detection radius. Heligoland could then give warning to London that a knock-out blow was imminent. At the cruising speed of a He 111, and depending on the flight path, that could be 1.5-2 hours additional warning (or even more if the bombers formed up in range of Heligoland). Very handy, even though the actual targets wouldn’t be known until the English coast was crossed.

Obviously, there are a whole bunch of caveats. I’m obviously assuming that, not only is Dutch neutrality respected (and the Low Countries not invaded, for that matter), but also that France has not been conquered. This is not our 1940, in other words, but a scenario often envisaged in the 1930s, where Germany suddenly attacks Britain without any warning. I’m also assuming that Germany doesn’t assault Heligoland first, or cut its communications with Britain (whether radio or cable).³ But even these acts would at least give warning that an attack was imminent, which is more than the British got in the usual nightmare imaginings. Finally, and perhaps least reasonably, I’m assuming that Britain (well, Australia) would not have handed it back to Germany. Heligoland in foreign hands would have been a major irritant to German nationalists, and unlike the case with the ex-German colonies, Hitler wouldn’t have been merely posturing when he said he wanted it back. So, very likely, giving it back to Germany would probably have been one of the first acts of appeasement.

The only reason to keep it, frankly, would be as an early warning post. Even then, would the Air Ministry risk placing such a valuable piece of technology as radar right under the German’s noses, where they could study its emissions at their leisure and quickly capture it in wartime?⁴ Probably not. Though even without RDF (which in any case was secret until 1941), the British public might gain some measure of confidence, whether false or not, just from being told that there were ‘observers’ on Heligoland who would give advance warning of a massive aerial armada heading their way.

Still, it would seem that, even in this alternate history, the Heligoland Mandate would have come to exactly nothing in the end, just as it did in ours. An interesting and diverting nothing, though.

Image source: Norman Macmillan, The Chosen Instrument (London: John Lane The Bodley Head, 1938), 21.

1. Margaret MacMillan, Peacemakers: The Paris Conference of 1919 and Its Attempt to End War (London: John Murray, 2002), 187.
2. Chain Home Low, for detecting low-level aircraft, had a much shorter range. But it would still cover a useful area of sea.
3. Another thought: a German army which had prepared for an opposed landing on Heligoland might also be a bit better prepared for an opposed landing in Kent …
4. Germany had radar too, of course, but they did not well understand the capabilities of the British system or how it would be used — even after the Graf Zeppelin II made several trips parallel to the English coast, loaded with radio detection gear, in what must have been among the first ELINT air missions ever.

[Cross-posted at Revise and Dissent.]

Recently, I read Alan Kramer’s Dynamic of Destruction: Culture and Mass Killing in the First World War. It’s an excellent book, both illuminating and informative (being airminded, I found the section on the Austrian and German bombing of Italy to be especially fascinating), and I highly recommend it.¹

But there was one section which brought me up short. In a section on Britain’s entry into the war, Kramer says that the breach of Belgian neutrality by Germany was a gift to Asquith and Grey, because it meant that the war could be framed as a just war. Absolutely. Then he goes on to say:

At the time, British decision-makers could only sense intuitively what we know today — this was far more than a conservative defence of the status quo: had Germany succeeded at the Marne in September 1914, which it almost did, the defeat of France and a separate peace would have been followed by a defeat of Russia and, after a pause to build up the German navy, the invasion of Britain from a position of towering strength on the Continent.²

Which is where I went ‘Huh?’ Do we really know that? Because I didn’t know we knew that.

It’s not that the scenario outlined is implausible — I’m just not sure how it can be elevated to the status of fact. OK, let’s walk through it. (This is all my speculation, as Kramer doesn’t explain his reasoning.) So Germany wins the Battle of the Marne, takes Paris, forces France to surrender late in 1914. By this time it’s winter, too late to take on Russia in any serious way. But around May 1915, the bulk of the Germany army could have transferred to the east and, let’s assume, crushes Russia by the end of the year, about 2 years before it was historically out of the war. It’s really only at this point that Germany could afford to start building up for an invasion of Britain. That means dreadnoughts, above all, to secure sea superiority in order to get its troops across and supply them.³ And Britain had a massive advantage here: 22 dreadnoughts to Germany’s 13 in August 1914, and was building them at a faster rate.⁴ But let’s make a wild assumption and grant Germany the ability to build to a superiority in dreadnoughts in one cycle of construction, about 2.5 years or so. So we’re now looking at the middle of 1918: just about the earliest that Germany could possibly be ready to invade Britain in overwhelming strength, about 4 years since the invasion of Belgium and France.

But what’s Britain been doing in all that time? I rather doubt it’s been sitting on its hands, whether it’s a belligerent or a neutral. It would absolutely have been building up the navy; that would have been uncontroversial while so long as Germany was overrunning Europe. But anyway, I’ve magically waved away Britain’s naval superiority, so the main question is what would have happened with the army? Presumably it would have been expanded, but on a volunteer or a conscription basis? Let’s say it’s a volunteer force (though if the Unionists had come in in the election due by 1916, conscription probably would have too) — relatively small, but far larger than the home forces in 1914. There might also have been contingents from the Empire too. In the real war, about one million men volunteered by January 1915, so when all is said and done, I’d say Britain could have sustained an army of something approaching a million volunteers for home defence. That is not an inconsiderable force, especially considering that it’s had 3 or 4 years to dig in. It’s true that Germany would have had a much bigger, veteran army, and I’m assuming that it would have had the power to transport and supply a big army due to its naval buildup. But given the superiority of the defence at this time, perhaps especially for contested landings (how did Gallipoli go again?), it’s hard to see how it can be assumed that the Germans would want to chance it.⁵

What else might they have done? Well, tried to strangle Britain economically, by U-boat. Already in 1915, U-boats accounted for over a million tons of Allied shipping, so in this alternate timeline, the Germans would have known that their submarines had a good chance of success.⁶ If they’d poured resources into U-boats instead of dreadnoughts, and used bases in France to extend their reach into the Atlantic, then surely there’s every chance that Britain would have been on its knees at some point in 1917. After all, it practically was in our 1917, with France and Russia both still in the war.

Well, maybe not. I’m sure my alternate alternate history can be picked to pieces as well,⁷ but I think I’ve made my point: we don’t know that a German invasion of Britain would have followed from a French defeat in 1914. There are too many imponderables, there’s reasonable doubt. Maybe it would have happened that way; and almost certainly, whatever happened would have been bad for Britain. So I agree with Kramer that Britain didn’t have much choice about whether to enter the war, strategically speaking, but I don’t agree that we know much beyond that.

That’s only one paragraph, though — do read the rest of the book :)

1. Reading really good books is depressing when you’re in the middle of writing a thesis — Nicoletta F. Gullace’s “The Blood of Our Sons”: Men, Women, and the Renegotiation of British Citizenship During the Great War (New York and Basingstoke: Palgrave Macmillan, 2004) was another. Which suggests a New Year’s resolution: to read only rubbish …
2. Alan Kramer, Dynamic of Destruction: Culture and Mass Killing in the First World War (Oxford: Oxford University Press, 2007), 95.
3. Air superiority would have been nowhere near as important as it was in 1940, since the use of aircraft against ships was in its infancy at the time.
4. 13 under construction by Britain, 5 by Germany. Paul G. Halpern, A Naval History of World War I (Annapolis: Naval Institute Press, 1994), 7.
5. The ultimate success of such an invasion is another question, but Kramer doesn’t actually say that it would necessarily have been successful — though I think it’s implied.
6. Though if Britain had remained neutral, then the U-boat would have had far fewer targets and so fewer chances to prove themselves …
7. What’s Italy doing? If it joins in with the Central Powers in 1915, Britain’s naval superiority vanishes, unless it abandons the Mediterranean entirely. Or, maybe Germany would pursue both tracks (invasion and strangulation) at once, as in 1940, with U-boats taking the place of bombers. And so on.

WHAT AUSTRALIA WOULD BE LIKE UNDER HUN RULE. — An original recruiting poster which was used with great success in South Australia. Tasmania, it will be noted, becomes Kaisermania, and the idols of the Huns have provided other place-names.

This is from the Daily Mail, 3 July 1917, p. 8, and would appear to be a South Australian recruiting poster, showing how the map of Australia might be redrawn if Germany won. Australia itself becomes “New-Germany”; Perth becomes Tirpitzburg; Adelaide, Hindenburg; Brisbane, Bernhardiburg; Sydney, Nietscheburg [sic]; Tasmania (not Hobart), Kaisermania; and, most appropriately from my point of view, Melbourne would be renamed Zeppelinburg!

I don’t think much has been written on German plans for Australia in the event of victory in the First World War, probably because the Germans themselves gave very little thought to the place. However, it seems unlikely that Germany would have wanted to take over Australia lock, stock and barrel; better to turn us into some sort of client state instead. They’d probably have wanted to take a few of Britain’s colonial possessions in the area, and perhaps would have insisted upon reparations or favourable trade terms. And our battlecruiser HMAS Australia — which caused von Spee such headaches in 1914 — would no doubt have had to go. No independent foreign policy, perhaps (not that we had much of one as it was!) But we probably wouldn’t have had to go so far as to need to translate such phrases as “don’t come the raw prawn with me, mate” into German — fortunately!

This idea that we had to fight Germany in France in order to prevent the Kaiser’s victory parade down Swanston St had obvious potential as a motivational device, and was used in stories and films as well. Did people really believe it? The Daily Mail said that the poster had ‘great success’, so perhaps they did.