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Abraham Wald's Work on Airplane Survivability (1984) [pdf] (ucsc.edu)
23 points by tjalfi 23 days ago | hide | past | favorite | 14 comments



It's a work that people love to make Youtube videos out of, and is interesting. "Where are the missing bullet/flak holes?" is the question people should be asking, rather than just armoring the places that are obviously bullet-ridden. The paper is much more technical than you would think from the popular tale (Lagrange multipliers, etc).

I believe they did other story-worthy statistical feats, like estimating the size of the German tank fleet by observing the serial numbers of captured tanks.


Aahh, yes, the German Tank Problem[1]. Also more complex than it would initially seem.

[1] https://en.wikipedia.org/wiki/German_tank_problem


I read about this in Daniel Kahneman's "Thinking Slow and Fast" where this was listed under possible "suvivorship biases" i.e. we draw conclusions from data that survives but forget about the unseen data. For example, we read stories about how someone with a simple startup idea became a millionaire but never hear about those who tried and failed hence creating a biased view on startups.


(submitter)

Wald's WWII memos were reprinted in the 1980s and are available here[0].

[0] https://web.archive.org/web/20140814122810/https://www.cna.o...


I study WW2, and the US had such fundamental problems with bomber design that you could say they were of doctrine in nature.

The B-17 "Flying Fortress" had lots of guns and a crew of 10, but couldn't defend itself against German fighters. It's payload ended up being the same as the 2-man British Mosquito bomber.

The B-29 was the first pressurized bomber, yet that just made it expensive to build since bombing accuracy at 20k feet is random, and Curtis Lemay ended up using it at 5k feet, with napalm.


> The B-17 "Flying Fortress" had lots of guns and a crew of 10, but couldn't defend itself against German fighters. It's payload ended up being the same as the 2-man British Mosquito bomber.

To make a more apples to apples comparison, one should replace the B-17 with the British heavy bombers, who often flew on the same missions as the Mosquito. The British heavies were similar to the American ones (though somewhat higher bomb load and less defensive guns). The interesting thing is that the loss rate for the Mosquito was an order of magnitude less than for the heavies (which was beyond appalling). It was just so fast that it was very difficult to catch for the Luftwaffe night fighters, and of course by being faster it spent less time in flak barrages as well.

Of course one could argue that the slow heavies presented much juicier and easier targets for the Luftwaffe and the flak, so they didn't bother going after the Mosquitos. And thus if Bomber Command had switched from heavies to fast unarmed ones like Mosquito the loss rate would have climbed. Still hard to see how it could have reached the levels it factually did for the heavies.

An interesting tidbit here is from Freeman Dyson, who served as an analyst in Bomber Command during the war. He had calculated that the loss rate would be reduced by removing all, or most, defensive armaments. This was based on reduced drag and weight increasing the speed, and also that interviews with aircrew who had been shot down and (miraculously) survived and made it back to England revealed that most never knew what hit them. But this proposal was shot down, as the myth of the heroic gunners protecting their mates was so strong.


interviews with aircrew who had been shot down and (miraculously) survived and made it back to England revealed that most never knew what hit them

The particularly depressing part of this story is that for months RAF crews were reporting attacks they couldn't see coming, and the RAF ignored these reports and chalked these losses up to flak. What was happening was the Luftwaffe had observed that RAF heavy bombers lacked belly gun turrets and had essentially zero downwards visibility, and had developed the upwards-facing Schräge Musik gun mounts to attack from below. What was also happening was that RAF bombers were being equipped with Monica tail warning RADAR in an attempt to detect pursuing night fighters more easily, but the Luftwaffe had quickly developed detectors that allowed night fighters to directly home in on these bombers instead, while still avoiding being detected by Monica sets. Together, these were responsible for much of the severe losses suffered by Bomber Command in the winter of 1943-1944.


> Luftwaffe had observed that RAF heavy bombers lacked belly gun turrets and had essentially zero downwards visibility, and had developed the upwards-facing Schräge Musik

My understanding was that the point behind attacking from below wasn't so much the bombers lacking a belly turret as the bomber being silhouetted against the night sky, whereas detecting a plane by looking downwards towards the dark earth was almost impossible.

And yeah, the history of early electronic warfare is fascinating. All the things they came up with, and the counter-measures developed amazingly quickly etc.


There were plenty of other reasons to attack from below - interest in the tactic predates the war - but I don't think the tactic would have been anywhere near as effective if RAF heavy bombers had been equipped with belly turrets (and armed with something better than the basically useless .303 machine guns). Entirely different tactics were used against the USAAF formations in daylight, where a slow overtaking approach from below would be far to vulnerable.

whereas detecting a plane by looking downwards towards the dark earth was almost impossible

This would be true on the long approach to the target, but once near the target area, bombers would be silhouetted from below by searchlights, flares, and the burning city beneath them. Enough light was available from these sources for the Luftwaffe to use Wilde Sau single-seat "day" fighters at night.


US had such fundamental problems with bomber design that you could say they were of doctrine in nature

The B-17 "Flying Fortress" had lots of guns and a crew of 10, but couldn't defend itself against German fighters

These are major oversimplifications. The USAAF doctrine, along with pretty much everyone else in the 1930s, was based on the idea that "the bomber always gets through" and that fighter and AAA (anti-aircraft artillery) would not be able to prevent bombers from reaching their targets in daylight. At the same time, USAAF strategy was constrained by the ranges expected for a campaign in the Pacific theater, necessarily requiring a longer-ranged aircraft that could not hope to be escorted by fighters. In that context, a bomber (exemplified at the time by the B-17) would have to bring its escort along with it - hence armor, heavy defensive armament, and tight combat box formations with overlapping fields of fire.

Fast forward several years, and the first year of WWII largely confirmed this doctrine, but with major caveats. Luftwaffe bombers had operated with impunity over continental Europe, and even when faced with a coordinated, RADAR-directed RAF fighter defense, they did not fail to reach their targets. What had not been expected pre-war was that this bombing would not end wars immediately, that civilian populations and industry were far more resilient than expected, and that "the bomber always gets through" did not mean that bomber losses would be acceptable in a war of attrition (indeed, losses to aircrew and aircraft would quickly limit what operations could be performed).

In light of this development, the RAF abandoned the idea of daylight bombing entirely and put their hopes in night attacks, ignorant of the extremely poor accuracy they would achieve and the strength the Luftwaffe would soon develop in RADAR-guided night fighters. Guns and armor were traded for greater bombload, but until the wholesale switch to "area bombing" and incendiaries, most of those bombs were being wasted in the German countryside. The USAAF slogged on, hoping that daylight firepower would be enough. In the end, it wasn't - losses to unescorted missions to major strategic targets were just too high - but those losses were the result of virtually the entire Luftwaffe fighter and AAA force being retasked to defend German cities and industry - consider the desperate lengths the Luftwaffe was willing to go in search of anything to counter them (near-suicidal single-use rocket rams, huge cannon in the hopes of outranging defensive armament, etc). Once escorting fighters became available in early 1944, USAAF daylight bombing became a tool not for destroying German industry, but for destroying the Luftwaffe and ensuring air superiority.

The B-29 was the first pressurized bomber, yet that just made it expensive to build since bombing accuracy at 20k feet is random, and Curtis Lemay ended up using it at 5k feet, with napalm

The B-29 was designed with several lessons in mind:

1 - AAA and fighters strugged to reach higher altitudes effectively (B-17s already flew high enough to challenge the fighters available to the Axis) so increasing service ceiling even higher would move bombers out of range of existing AAA and fighters. Reaching higher altitudes with AAA requires larger and larger guns that are correspondingly more expensive, less mobile, and easier to target in return. (Compare the road-mobile size of the 88mm FlaK-18/36/37 versus the much larger and functionally stationary 128mm FlaK 40) Fighters would struggle to reach these altitudes to intercept as well, and anything optimized for such high altitude combat would likely struggle at lower altitudes where it would be vulnerable to other fighters.

2 - The realization that war against Germany might need to be conducted without bases in the UK and that war with Japan would need to be conducted without bases in the Phillipines. This would require much greater range than any existing bomber.

Unsurprisingly, given the challenges of these requirements the B-29 was difficult to develop - the program actually costing more than the Manhattan project - and not really complete until the definitive post-war B-50. In practice, the great range would not be needed in the European theater, and the threat of Japanese fighters and AAA was greatly overestimated based on experience in Europe. In light of minimal opposition, B-29s traded guns and armor for greater bombloads and attacked at lower altitudes (often at night to reduce the fighter threat).


> The USAAF doctrine, along with pretty much everyone else in the 1930s...

I don't think anybody disputes what the pre-war bomber doctrine was. The criticism, IMHO, is that when TSHTF and reality showed that the doctrine wasn't worth the paper it was written on, they didn't change anything, just bit their tongues and pressed on, at enormous expense in manpower and materiel.

Not saying it would have been easy (or even realistically doable) to turn around industrial production, crew training, and doctrine in the middle of a major war. But still..

Also, not saying all strategic bombing was pointless and ineffective. Hitting the refineries in Ploesti, the aerial mining of the Danube were highly effective.


It's easy to look back with the benefit of hindsight to say that doctrine needed to change faster, but the realities of the war made that a challenge.

The lessons of 1940 should have been "build long-range escort fighters ASAP!", but it's also understandable that USAAF planners looked at the weak defensive armament, lower altitudes, and poor formation planning of Luftwaffe and RAF bombing operations and thought their equipment and tactics would perform differently. There is also the "what else can we do?" aspect to this strategy - 1943 was too early to mount an invasion of western Europe, the campaign in Italy beginning to stall - and the US and UK were left with few means of tying down German resources to prevent them from being sent to the eastern front. There was definitely some sunk-cost fallacy "we've spent all the time and resources building the 8th Air Force, so we're going to use it", but on a strategic level there weren't a lot of clearly better options prior to 1944.

The strategic bombing offensive didn't really get up to full strength until 1943, and by later that year it was finally clear that unescorted bombers would suffer unsustainable losses. Long-range escort fighters simply didn't exist in-theater in quantity until late 1943/early 1944. Once those fighters were available, tactics absolutely changed, first with close escort of bomber formations, and then by freeing the fighters to range ahead of the bombers to strike air defense targets and break up approaching fighter formations.


Sure, it's easy to play armchair general after the fact. With that caveat out of the way, as an alternative history if the generals had realized the great cost of unescorted bombing raids and the generally poor effectiveness of WWII strategic bombing:

Generally, scale back the size of the heavy bomber force and spend the resources on other things. E.g. Bomber Command consumed up to 50% of the total British war effort, a staggeringly high number. On a bad night, BC lost more aircrew than Fighter Command during the entire Battle of Britain. And then they just shrugged and did it again a week later. And all this mostly for firebombing civilians with very low military effect to boot.

So what else to spend resources on. E.g.

- Win the Battle of the Atlantic faster. E.g. more destroyers (and later escort carriers). Large four engine planes equipped with radar and depth charges made life very sour for u-boats.

- Spend more resources in the Mediterranean front to push faster into Italy. Maybe even make an effort to retake Crete and Greece.

- Use the (reduced size) heavy bomber fleet for attacking targets close enough that they could be escorted by fighters. Say, any German military presence in Northern France; airfields, ports, transportation infrastructure like bridges or railway yards, fuel depots.

All in all, if the Allies had played all their cards better, maybe they could have done D-day already late summer '43?

Of course, similarly, had the Germans played their cards better they could, if not win the war outright, at least prolong it. Or they could have played their cards even better and not let those Nazi thugs take power in the first place, ideally avoiding the entire war.


There are a number of interesting what ifs to consider.

Generally, scale back the size of the heavy bomber force and spend the resources on other things

Absolutely, at least for the RAF. Coastal Command was denied long-range bombers for far too long, and these aircraft were absolutely critical for winning the battle of the Atlantic.

Spend more resources in the Mediterranean front to push faster into Italy. Maybe even make an effort to retake Crete and Greece

Churchill was enamored with these ideas (US leaders deeply opposed to what was perceived as an attempt at protecting spheres of influence rather than winning the war), but I don't think more resources in the Mediterranean would have necessarily achieved much more. Italy is just terrible ground to fight over, with numerous mountain ranges that allow small defensive forces to delay an invader. Much of the most painful parts of the campaign (ex Salerno, Anzio) had to be conducted without the kind air superiority that would be present later in the war, since the Mediterranean theater is just a difficult place from an aviation standpoint: far enough to be difficult to maintain fighter coverage, near enough to be in easy bomber range, and not quite big enough for carrier groups at the time to fight effectively. There also were often simply not enough resources to pursue both a broader Mediterranean strategy and an invasion of western Europe.

Use the (reduced size) heavy bomber fleet for attacking targets close enough that they could be escorted by fighters. Say, any German military presence in Northern France; airfields, ports, transportation infrastructure like bridges or railway yards, fuel depots

While the large daylight attacks over Germany tend to overshadow everything else, plenty of 8th Air Force missions were over closer targets in France, as well all of the 9th "tactical" Air Force missions that were necessary to strike smaller tactical targets (airfields, RADAR stations, bridges, rail yards). In light of postwar surveys, using strategic bombers to strike small targets was a gamble, so it's not clear that much more would have been achieved. In addition, targets across all of France and the low countries needed to be struck to reduce German strength and reserves while also not disclosing the specific target of D-day.

All in all, if the Allies had played all their cards better, maybe they could have done D-day already late summer '43?

The US army really wanted to an invasion in 1943, and had to be restrained from it by practical constraints. Logistics of a massive assault on defended beaches with no hope of quickly capturing a usable port just weren't ready until 1944. Even with all the preparation, the Allied advance in summer/fall of 1944 was severely hamstrung by logistics.




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