Monday, June 9, 2014

Normandy+3: The Fatherland Sends Its Best Regards

I am sure I've done this one before, because I distinctly recall cringing at the introductory, " Bertold Brecht said..." I just like this version a little better than Stan Roger's original, just like I prefer this version of Northwest Passage. My apology for the repetition is that it was that or this.

Call me a Gen Xer, but I prefer Rogers to Lightfoot. Plus, the Mary Ellen Carter rises again.

Let me put this in bald terms once again. Human society tends to get itself levered into corners where state orders can find their only escape in war. The question is: how do state orders get actual people to fight their wars for them? And by actual people, I mean until now above all young men. The conventional answer is that young men are stupid, and can be manipulated into making war. Stupid, stupid young men. 

Without at all denying that young men tend to be stupid, I propose that this is a little simple-minded, that young men have some agency after all, and historically have often declined to take part in the wars of state orders. 

Last time, I tried to connect Bernard Montgomery to Prince Eugen of Savoy. The connection was a musical link, so the connection more specifically implied is the 1717 siege of Belgrad with the 1944 invasion of Normandy. Nor am I entirely relying on a logically-illegitimate poetic convergence of a cover of "It's Raining Men" with the Prinz Eugenlied. 1717 was the last act in a generation of war that broke though constraints on manpower mobilisation that had held since Roman times. The great wars of the turn of the Eighteenth Century reached the limit of available manpower before they reached the limit of available money. The winning hand in the labour negotiation was thrown from finance to labour, and labour was allowed to negotiate its terms. 

Labour got what it wanted out of the War of the Spanish Succession: and so it remained through the Victory Campaign in Northwest Europe. My claim: these are the bookends of an era in which the state had to offer skilled trades learning on an as-offered basis in order to obtain the labour it needed to make war. 

Having set up the problem over the last three weeks to the limit of my poor narrative ability and available time, it is time for the payoff: sequels to the set-up. 

This is a sequel to D-3. I know, I know. It should be a sequel to D-15, but, like I said, I'm reaching the limits of my ability to organise myself. It is time to talk about the defeat of the oyster mine.

 Travel writer Saneka  includes this picture of the arches at Etretat, Normandy, in an article for that does not really seem to fit the implied mandate of the site. It is not as though this town is obscure. You are not going to understand Normandy unless you understand that it is close to Paris. That goes for the invasion, it goes for "the Normans," and it goes for 1066. It also goes for Etretat's tourist trade, but I digress. The point, other than a bit of scenery porn, is that this is a classic mining coast, with lots of shallow water that large ships have to cross in order to unload their cargoes, under threat from bottom-laid influence mines all the way. 

Big deal: I am not talking about strategy, but about the bargain: the "economy of knowledge." 

First, the problem: 

By early 1944, the combined acoustic-pressure “oyster” mine had been developed, and production was pressed against an emergency. By then 4,500 had been manufactured, and 2000 were sent forward to a depot at Le Mans. The Luftwaffe was finally briefed on the nature of the weapon in April, and in May “Goering” directed their return to Germany. The depot had been cleared by 4 June, and none had been laid prior to the invasion. By contrast, by the end of July, 5000 had been laid.

 But, as the official history says, the Allies were already familiar with the pressure type, and although no means of sweeping them had been found, appropriate countermeasures were in place, such as limits on ship speeds. “It was not until after the war that the Germans knew how badly the ‘oyster’ had failed in Seine Bay.” 

Although the fact that the invasion succeeded might have given them some intimation. During the final phase of the war, 8000 mines were laid, 1300 near the coast of England, 600 by E-Boats and 750 by aircraft, the balance going into the Scheldt and “assault area.” Frustratingly, the history gives no count of shipping sunk off the assault area, as it was not civilian shipping. It does note, 290, that there were 955 minesweepers in home waters and 1520 abroad in “1944.” There’s a also a table, deep in volume II that tends to show that the German mining effort in June-July was very heavy, and that the reward was very low. This counts as a success –but only to the extent that countermeasures did not reduce tonnage deliveries. Forcing hard-to-come-by freighters to sail very slowly is an excellent way of reducing tonnage deliveries, and the whole point of actuation counters is to create a "sustained attrition" minefield which reduces enemy activities over time. (Though of course I am introducing a replacement metric of deliveries to the ship loss metric here used by the Historical Branch of the Naval Staff.)*

This is how management talks: the problem was met with outstanding success, and the actual skill involved in doing so is invisible. No need for pay raises or short-selling the stock!

The German oyster mine was a combined pressure-and-acoustic triggered air-dropped mine. As far as I know, there is no discussion of its capabilities readily available on the Internet, but I have lucked onto an online posting of the United States Navy's mine manual, so we can look at the Type 52 instead.

The Type 52 was a 1000lb air-dropped modular-actuated mine with pressure, acoustic and other firing choices, containing 625lb of HBX-1, one of the new generation of explosives discovered to be mass synthesisable alongside RDX. It is not much to look at

but then it wasn't supposed to be  a visual treat. The arming mechanism includes a delay, a sterilisation clock, a ship counter, and a five-position adjustable sensitivity control. Taken together, a pretty good example of mid-century watchmaking design. (By which I rather loosely gather together all the techniques that had been developed to implement watch-like outcomes. I imagine that it may well have been an electrical, rather than mechanical device.) Notice that the Mod 4, fired by "combined pressure and acoustic actuation" is far less susceptible to current and wave effects than previous generations. Given offensive minelaying by brief intrusions into enemy controlled waters, this is pretty much the necessary requirement for a mine attack on shipping off the Normandy coast. It is, in turn, what makes this mine so dangerous. Sweeping, in turn, requires "artificially generated pressure and acoustic signals" of the precise kind "programmed" (to use an anachronistic turn of phrase) into the firing mechanism. Notice that an upgrade that combines acoustic, pressure and magnetic influences is eminently possible. Even if the Germans did not deploy such a weapon, the ability to counter it is a prerequisite for a successful Normandy invasion.

Yet that is precisely what the Allies did. How? In part, with specially reinforced "minebreakers," but mainly with sweepers set to exactly the necessary combination of signals. Something that was only possible because the Allies could reliably find and dismantle a proportion of the mines used in the attack and use these settings on their sweepers. They hunted mines, as well as sweeping them.

How did they do this? With sonar. 

Now, let us look at that, by reference to the same invaluable site, the 1953 Naval Sonar textbook for reserve officers. 

The basic principle of sonar is well-known. An artificial inducer is used to produce a relatively narrow beam of ultrasonic waves which, when impinging on objects in the water, is reflected back to a receiver. The ultrasonic waves are then electronically filtered, amplified, and frequency-shifted to produce a variety of indicators. These of course include the visually iconic headset-rendered "ping."

The ping was the first iteration of sonar technology, available towards the end of WWI, but it had clear limitations as a tool of battle management. The same signal could be used to produce everything from a little light in an indicator to a cathode ray trace, but the great minds of the Gunnery division had already concluded, in an analogous case, that a trace recorder was the way to go. (If you have ever wondered how those battle maps in a typical history of a World War I/II naval battle are produced --the kind that demonstrate that no-one had any idea where there ship actually was at Cape Esperance or Jutland-- thank the bulging brains at the top of the academy graduation list for them.) 

The battle trace recorder is a pretty simple device, looking back from our lofty perch. A roll of "chemically treated paper" is drawn by a motor past a stylus which deflects up and down depending on the amplitude of the signal from the sonar receiver, producing a time-and-distance chart that gives the combat information centre a continuous trace of where the target is. For a mine, which is not moving, diving, or doing anything else to hide, the salience of this trace is that it allows one to get through the noise and clutter and turn an uncertain fix into a clear idea of where the mine might be, at which point you can send divers down. The trace recorder, in short, applies the power of "memory" (this time using a contemporary analogy) to the problem of finding sonar targets.

It is, however, more complicated than that, because actually the information on the trace recorder is a time and bearing trace. As we know from our lived experience, bearing is turned into range by means of a spread set of detectors. In our eyes, but not our ears, a "right" channel and a "left" channel are combined in a process that is much more complicated than introductory optics might suggest in order to suppress external noise and compensate for the limits of the detectors.

I chose this illustration to make it seem more complicated. Oh, wait, no I didn't. This is complicated.
It gets even more complicated! The state of the art by 1953 --I am inferring, by 1944, but might be wrong-- was an fm scanning sonar. The scanning sonar part is just making the process faster and more efficient. The "fm" part is the same as in fm radio. Frequency modulation is used to get more information out of given wavelength range than amplitude modulation will allow. I think? Me not radio engineer!

So, basically, we send out a narrow beam of sound. It bounces off the target, is picked up by a receiver, and then is put through even more resistors and inductors, producing a more useful output. This is pretty tricky. By 1944, sonars are being asked to output positive indicators at 20 decibels below the performance required for submarine detections in 1939. At this point, reverberation is the main source of noise, and the design requirement is a continuous variation of gain through the period of the ping. Don't look at me like that --I'm just quoting by this point.

Here's a schematic picture, in this case of the QGB standard sonar set, which, from the name, I would guess is a British equipment, since an American one would have a name like "QG
-213-Mod 1A." 

This is probably enough details and pictures. You will, of course, find much more at the link. The point, very simple, to take away here is that this manual explains theory and mechanism to naval reserve officers and provides them, and the tradesmen they command, how these devices are supposed to work; and so, of course, how to repair these fractious devices when a vacuum tube blows out, as it inevitably will. 

I have harped on this point before, and probably will again, but I cannot emphasise it enough: the Navy is paying people to design, operate and repair equipment that turns sound into electronic signals, and then back again. People who are alive, and working in various industries in the 1950s. 

You know, industries like television and music recording. I say again, because I never tire of hearing myself say it, that you will never understand the postwar transformation of the everyday life of our society (and the everyday work of the people who get paid to make it function) until you understand the transformation worked by World War II. 

Eric Grove, ed. Defeat of the Enemy Attack on Shipping, 1939—1945: A Revised Edition of the Naval Staff History Volumes IA (Texts and Appendices) and IB (Plans and Tables) (Aldershot, Hamps.: Ashgate for the Naval Records Society, 1997; original edition 1957): Chapter 22 (174ff). Details of the "last phase of the German minelaying offensive" begin, 200.

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