Prominent physicist Freeman
Dyson recalls the time he spent developing analytical methods to help
the British Royal Air Force bomb German targets during World War II.
I began work in the Operational Research Section (ORS) of the
British Royal Air Force’s Bomber Command on July 25, 1943. I was 19
years old, fresh from an abbreviated two years as a student at the
University of Cambridge. The headquarters of Bomber Command was a
substantial set of red brick buildings, hidden in the middle of a forest
on top of a hill in the English county of Buckinghamshire. The main
buildings had been built before the War. The ORS was added in 1941 and
was housed in a collection of trailers at the back. Trees were growing
right up to our windows, so we had little daylight even in summer. The
Germans must have known where we were, but their planes never came to
disturb us.
Air War: A British Lancaster bomber is silhouetted against flares and
explosions during the attack on Hamburg, Germany, on the night of
January 30, 1943. (Credit: Imperial War Museum)
I was billeted in the home of the Parsons family in the village of
Hughenden. Mrs. Parsons was a motherly soul and took good care of me.
Once a week, she put her round tin bathtub out on her kitchen floor and
filled it with hot water for my weekly splash. Each morning I bicycled
the five miles up the hill to Bomber Command, and each evening I came
coasting down. Sometimes, as I was struggling up the hill, an air force
limousine would zoom by, and I would have a quick glimpse of our
commander in chief, Sir Arthur Harris, sitting in the back, on his way
to give the orders that sent thousands of boys my age to their deaths.
Every day, depending on the weather and the readiness of the bombers, he
would decide whether to send their crews out that night or let them
rest. Every day, he chose the targets for the night.
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“Bomber” Harris’s entire career had been devoted to the proposition
that strategic bombing could defeat Germany without the use of land
armies. The mammoth force of heavy bombers that he commanded had been
planned by the British government in 1936 as our primary instrument for
defeating Hitler without repeating the horrors of the trench warfare of
World War I. Bomber Command, by itself, was absorbing about one-quarter
of the entire British war effort.
The members of Bomber Command’s ORS were civilians, employed by the
Ministry of Aircraft Production and not by the air force. The idea was
that we would provide senior officers with independent scientific and
technical advice. The experimental physicist Patrick Blackett had
invented the ORS system in order to give advice to the navy. One of the
crucial problems for the navy was to verify scientifically the
destruction of U-boats. Every ship or airplane that dropped a depth
charge somewhere near a U-boat was apt to claim a kill. An independent
group of scientists was needed to evaluate the evidence impartially and
find out which tactics were effective.
Bomber Command had a similar problem in evaluating the
effectiveness of bombing. Aircrew frequently reported the destruction of
targets when photographs showed they had missed by several miles. The
navy ORS was extremely effective and made great contributions to winning
the war against the U-boats in the Atlantic. But Blackett had two
enormous advantages. First, he was a world-renowned scientist (who would
later win a Nobel Prize), with a safe job in the academic world, so he
could threaten to resign if his advice was not followed. Second, he had
been a navy officer in World War I and was respected by the admirals he
advised. Basil Dickins, the chief of our ORS at Bomber Command, had
neither of these advantages. He was a civil servant with no independent
standing. He could not threaten to resign, and Sir Arthur Harris had no
respect for him. His career depended on telling Sir Arthur things that
Sir Arthur wanted to hear. So that is what he did. He gave Sir Arthur
information rather than advice. He never raised serious questions about
Sir Arthur’s tactics and strategy.
Our ORS was divided into sections and subsections. The sections
were ORS1, concerned with bombing effectiveness; ORS2, concerned with
bomber losses; ORS3, concerned with history. My boss, Reuben Smeed, was
chief of ORS2. The subsections of ORS2 were ORS2a, collecting crew
reports and investigating causes of losses; ORS2b, studying the
effectiveness of electronic countermeasures; ORS2c, studying damage to
returning bombers; ORS2d, doing statistical analysis and other jobs
requiring some mathematical skill. I was put into ORS2d.
Two other new boys arrived at the same time I did. One was John
Carthy, who was in ORS1; the other was Mike O’Loughlin, who shared an
office with me in ORS2d. John had been a leading actor in the Cambridge
University student theater. Mike had been briefly in the army but was
discharged when he was found to be epileptic. John and Mike and I became
lifelong friends. John was cheerful, Mike was bitter, and I was
somewhere in between. In later life, John was a biologist at the
University of London, and Mike taught engineering at the Cambridge
Polytechnic. After retiring from the Polytechnic, Mike became an
Anglican minister in the parish of Linton, near Cambridge.
The ORS consisted of about 30 people, a mixed bunch of civil
servants, academic experts, and students. Working with us were an equal
number of WAAFs, girls of the Women’s Auxiliary Air Force, who wore blue
uniforms and were subject to military discipline. The WAAFs were
photographic interpreters, calculators, technicians, drivers, and
secretaries. They did most of the real work of the ORS. They also
supplied us with tea and sympathy. They made a depressing situation
bearable. Their leader was Sergeant Asplen, a tall and strikingly
beautiful girl whose authority was never questioned. The sergeant kept
herself free of romantic entanglements. But two of her charges, a
vivacious redhead named Dorothy and a more thoughtful brunette called
Betty, became attached to my friends John and Mike. Love affairs were
not officially discouraged. We celebrated two weddings before the War
was over, with Dorothy and Betty discarding their dumpy blue uniforms
for an afternoon and appearing resplendent in white silk. The marriages
endured, and each afterwards produced four children.
My first day of work was the day after one of our most successful
operations, a full-force night attack on Hamburg. For the first time,
the bombers had used the decoy system, which we called WINDOW and the
Americans called CHAFF. WINDOW consisted of packets of paper strips
coated with aluminum paint. One crew member in each bomber was
responsible for throwing packets of WINDOW down a chute, at a rate of
one packet per minute, while flying over Germany. The paper strips
floated slowly down through the stream of bombers, each strip a resonant
antenna tuned to the frequency of the German radars. The purpose was to
confuse the radars so that they could not track individual bombers in
the clutter of echoes from the WINDOW.
That day, the people at the ORS were joyful. I never saw them as
joyful again until the day that the war in Europe ended. WINDOW had
worked. The bomber losses the night before were only 12 out of 791, or
1.5 percent, far fewer than would have been expected for a major
operation in July, when the skies in northern Europe are never really
dark. Losses were usually about 5 percent and were mostly due to German
night fighters, guided to the bombers by radars on the ground. WINDOW
had cut the expected losses by two-thirds. Each bomber carried a crew of
seven, so WINDOW that night had saved the lives of about 180 of our
boys.
The first job that Reuben Smeed gave me to do when I arrived was to
draw pictures of the cloud of WINDOW trailing through the stream of
bombers as the night progressed, taking into account the local winds at
various altitudes as measured and reported by the bombers. My pictures
would be shown to the aircrew to impress on them how important it was
for them to stay within the stream after bombing the target, rather than
flying home independently.
Smeed explained to me that the same principles applied to bombers
flying at night over Germany and to ships crossing the Atlantic. Ships
had to travel in convoys, because the risk of being torpedoed by a
U-boat was much greater for a ship traveling alone. For the same reason,
bombers had to travel in streams: the risk of being tracked by radar
and shot down by an enemy fighter was much greater for a bomber flying
alone. But the crews tried to keep out of the bomber stream, because
they were more afraid of collisions than of fighters. Every time they
flew in the stream, they would see bombers coming close and almost
colliding with them, but they almost never saw fighters. The German
night fighter force was tiny compared with Bomber Command. But the
German pilots were highly skilled, and they hardly ever got shot down.
They carried a firing system called Schräge Musik, or “crooked music,”
which allowed them to fly underneath a bomber and fire guns upward at a
60-degree angle. The fighter could see the bomber clearly silhouetted
against the night sky, while the bomber could not see the fighter. This
system efficiently destroyed thousands of bombers, and we did not even
know that it existed. This was the greatest failure of the ORS. We
learned about Schräge Musik too late to do anything to counter it.
Smeed believed the crew’s judgement was wrong. He thought a
bomber’s chance of being shot down by a fighter was far greater than its
chance of colliding with another bomber, even in the densest part of
the bomber stream. But he had no evidence: he had been too busy with
other urgent problems to collect any. He told me that the most useful
thing I could do was to become Bomber Command’s expert on collisions.
When not otherwise employed, I should collect all the scraps of evidence
I could find about fatal and nonfatal collisions and put them all
together. Then perhaps we could convince the aircrew that they were
really safer staying in the stream.
There were two possible ways to study collisions, using theory or
using observations. I tried both. The theoretical way was to use a
formula: collision rate for a bomber flying in the stream equals density
of bombers multiplied by average relative velocity of two bombers
multiplied by mutual presentation area (MPA). The MPA was the area in a
geometric plane perpendicular to the relative velocity within which a
collision could occur. It was the same thing that atomic and particle
physicists call a collision cross section. For vertical collisions, it
was roughly four times the area of a bomber as seen from above. The
formula assumes that two bombers on a collision course do not see each
other in time to break off. For bombers flying at night over Germany,
that assumption was probably true.
All three factors in the collision formula were uncertain. The MPA
would be smaller for a sideways collision than for an up-and-down
collision, but I assumed that most of the collisions would be
up-and-down, with the relative velocity vertical. The relative velocity
would depend on how vigorously the bombers were corkscrewing as they
flew. Except during bombing runs over a target, they never flew straight
and level; that would have left them sitting ducks for antiaircraft
guns. The standard maneuver for avoiding antiaircraft fire was the
corkscrew, combining side-to-side with up-and-down weaving. For
predicting collisions, it was the up-and-down motion that was most
important. From crew reports I estimated up-and-down motions averaging
40 miles an hour, uncertain by a factor of two. But the dominant
uncertainty in the collision formula was the density of bombers in the
stream.
I studied the crew reports, which sometimes described large
deviations from the tracks that the bombers were supposed to fly. For
the majority of crews, who reported no large deviations, there was no
way to tell how close to their assigned tracks they actually flew. My
best estimate of the density of bombers was uncertain by a factor of 10.
This made the collision formula practically worthless as a predictive
tool. But it still had value as a way to set an upper bound on the
collision rate. If I assumed maximum values for all three factors in the
formula, it gave a loss rate due to collisions of 1 percent per
operation. One percent was much too high to be acceptable, but still
less than the overall loss rate of 5 percent. Even if we squeezed the
bomber stream to the highest possible density, collisions would not be
the main cause of losses.
How common, really, were collisions? Observational evidence of
lethal crashes over Germany was plentiful but unreliable. The crews
frequently reported seeing events that looked like collisions:
first an explosion in the air, and then two flaming objects falling to
the ground. These events were visible from great distances and were
often multiply reported. The crews tended to believe that they were
seeing collisions, but there was no way to be sure. Most of the events
probably involved single bombers, hit by antiaircraft shells or by
fighter cannon fire, that broke in half as they disintegrated.
In the end I found only two sources of evidence that I could trust:
bombers that collided over England and bombers that returned damaged by
nonlethal collisions over Germany. The numbers of incidents of both
kinds were reliable, and small enough that I could investigate each case
individually. The case that I remember best was a collision between two
Mosquito bombers over Munich. The Mosquito was a light, two-seat bomber
that Bomber Command used extensively for small-scale attacks, to
confuse the German defenses and distract attention from the heavy
attacks. Two Mosquitoes flew alone from England to Munich and then
collided over the target, with only minor damage. It was obvious that
the collision could not have been the result of normal operations. The
two pilots must have seen each other when they got to Munich and started
playing games. The Mosquito was fast and maneuverable and hardly ever
got shot down, so the pilots felt themselves to be invulnerable. I
interviewed Pilot-Officer Izatt, who was one of the two pilots. When I
gently questioned him about the Munich operation, he confessed that he
and his friend had been enjoying a dogfight over the target when they
bumped into each other. So I crossed the Munich collision off my list.
It was not relevant to the statistics on collisions between heavy
bombers in the bomber stream. There remained seven authentic nonlethal
collisions between heavy bombers over Germany.
For bombers flying at night over England in training exercises, I
knew the numbers of lethal and nonlethal collisions. After more than 60
years, I can’t recall them precisely, but I remember that the ratio of
lethal to nonlethal collisions was three to one. If I assumed that the
chance of surviving a collision was the same over Germany as over
England, then it was simple to calculate the number of lethal collisions
over Germany. But there were two reasons that assumption might be
false. On the one hand, a badly damaged aircraft over Germany might fail
to get home, while an aircraft with the same damage over England could
make a safe landing. On the other hand, the crew of a damaged aircraft
over England might decide to bail out and let the plane crash, while the
same crew over Germany would be strongly motivated to bring the plane
home. There was no way to incorporate these distinctions into my
calculations. But since they pulled in opposite directions, I decided to
ignore them both. I estimated the number of lethal collisions over
Germany in the time since the massive attacks began to be three times
the number of nonlethal collisions, or 21. These numbers referred to
major operations over Germany with high-density bomber streams, in which
about 60,000 sorties had been flown at the time I did the calculation.
So collisions destroyed 42 aircraft in 60,000 sorties, a loss rate of
.07 percent. This was the best estimate I could make. I could not
calculate any reliable limits of error, but I felt confident that the
estimate was correct within a factor of two. It was consistent with the
less accurate estimate obtained from the theoretical formula, and it
strongly confirmed Smeed’s belief that collisions were a smaller risk
than fighters.
For a week after I arrived at the ORS, the attacks on Hamburg
continued. The second, on July 27, raised a firestorm that devastated
the central part of the city and killed about 40,000 people. We
succeeded in raising firestorms only twice, once in Hamburg and once
more in Dresden in 1945, where between 25,000 and 60,000 people perished
(the numbers are still debated). The Germans had good air raid shelters
and warning systems and did what they were told. As a result, only a
few thousand people were killed in a typical major attack. But when
there was a firestorm, people were asphyxiated or roasted inside their
shelters, and the number killed was more than 10 times greater. Every
time Bomber Command attacked a city, we were trying to raise a
firestorm, but we never learnt why we so seldom succeeded. Probably a
firestorm could happen only when three things occurred together: first, a
high concentration of old buildings at the target site; second, an
attack with a high density of incendiary bombs in the target’s central
area; and, third, an atmospheric instability. When the combination of
these three things was just right, the flames and the winds produced a
blazing hurricane. The same thing happened one night in Tokyo in March
1945 and once more at Hiroshima the following August. The Tokyo
firestorm was the biggest, killing perhaps 100,000 people.
The third Hamburg raid was on the night of July 29, and the fourth
on August 2. After the firestorm, the law of diminishing returns was
operating. The fourth attack was a fiasco, with high and heavy clouds
over the city and bombs scattered over the countryside. Our bomber
losses were rising, close to 4 percent for the third attack and a little
over 4 percent for the fourth. The Germans had learnt quickly how to
deal with WINDOW. Since they could no longer track individual bombers
with radar, they guided their fighters into the bomber stream and let
them find their own targets. Within a month, loss rates were back at the
5 percent level, and WINDOW was no longer saving lives.
Another job that Smeed gave me was to invent ways to estimate the
effectiveness of various countermeasures, using all the evidence from a
heterogeneous collection of operations. The first countermeasure that I
worked on was MONICA. MONICA was a tail-mounted warning radar that
emitted a high-pitched squeal over the intercom when a bomber had
another aircraft close behind it. The squeals came more rapidly as the
distance measured by the radar became shorter. The crews disliked MONICA
because it was too sensitive and raised many false alarms. They usually
switched it off so that they could talk to each other without
interruption. My job was to see from the results of many operations
whether MONICA actually saved lives. I had to compare the loss rates of
bombers with and without MONICA. This was difficult because MONICA was
distributed unevenly among the squadrons. It was given preferentially to
Halifaxes (one of the two main types of British heavy bomber), which
usually had higher loss rates, and less often to Lancaster bombers,
which usually had lower loss rates. In addition, Halifaxes were sent
preferentially on less dangerous operations and Lancasters on more
dangerous operations. To use all the evidence from Halifax and Lancaster
losses on a variety of operations, I invented a method that was later
reinvented by epidemiologists and given the name “meta-analysis.”
Assembling the evidence from many operations to judge the effectiveness
of MONICA was just like assembling the evidence from many clinical
trials to judge the effectiveness of a drug.
My method of meta-analysis was the following: First, I subdivided
the data by operation and by type of aircraft. For example, one
subdivision would be Halifaxes on Bremen on March 5; another would be
Lancasters on Berlin on December 2. In each subdivision I tabulated the
number of aircraft with and without MONICA and the number lost with and
without MONICA. I also tabulated the number of MONICA aircraft expected
to be lost if the warning system had no effect, and the statistical
variance of that number. So I had two quantities for each subdivision:
observed-minus-expected losses of MONICA aircraft, and the variance of
this difference. I assumed that the distributions of losses in the
various subdivisions were uncorrelated. Thus, I could simply add up the
two quantities, observed-minus-expected losses and variance, over all
the subdivisions. The result was a total observed-minus-expected losses
and variance for all the MONICA aircraft, unbiased by the different
fractions of MONICA aircraft in the various subdivisions. This was a
sensitive test of effectiveness, making use of all the available
information. If the total of observed-minus-expected losses was
significantly negative, it meant that MONICA was effective. But instead,
the total was slightly positive and less than the square root of the
total variance. MONICA was statistically worthless. The crews had been
right when they decided to switch it off.
I later applied the same method of analysis to the question of
whether experience helped crews to survive. Bomber Command told the
crews that their chances of survival would increase with experience, and
the crews believed it. They were told, After you have got through the first few operations, things will get better.
This idea was important for morale at a time when the fraction of crews
surviving to the end of a 30-operation tour was only about 25 percent.
I subdivided the experienced and inexperienced crews on each operation
and did the analysis, and again, the result was clear. Experience did
not reduce loss rates. The cause of losses, whatever it was, killed
novice and expert crews impartially. This result contradicted the
official dogma, and the Command never accepted it. I blame the ORS, and I
blame myself in particular, for not taking this result seriously
enough. The evidence showed that the main cause of losses was an attack
that gave experienced crews no chance either to escape or to defend
themselves. If we had taken the evidence more seriously, we might have
discovered Schräge Musik in time to respond with effective
countermeasures.
Smeed and I agreed that Bomber Command could substantially reduce
losses by ripping out two gun turrets, with all their associated
hardware, from each bomber and reducing each crew from seven to five.
The gun turrets were costly in aerodynamic drag as well as in weight.
The turretless bombers would have flown 50 miles an hour faster and
would have spent much less time over Germany. The evidence that
experience did not reduce losses confirmed our opinion that the turrets
were useless. The turrets did not save bombers, because the gunners
rarely saw the fighters that killed them. But our proposal to rip out
the turrets went against the official mythology of the gallant gunners
defending their crewmates. Dickins never had the courage to push the
issue seriously in his conversations with Harris. If he had, Harris
might even have listened, and thousands of crewmen might have been
saved.
The part of his job that Smeed enjoyed most was interviewing
evaders. Evaders were crew members who had survived being shot down over
German-occupied countries and made their way back to England. About 1
percent of all those shot down came back. Each week, Smeed would go to
London and interview one or two of them. Sometimes he would take me
along. We were not supposed to ask them questions about how they got
back, but they would sometimes tell us amazing stories anyway. We were supposed
to ask them questions about how they were shot down. But they had very
little information to give us about that. Most of them said they never
saw a fighter and had no warning of an attack. There was just a sudden
burst of cannon fire, and the aircraft fell apart around them. Again, we
missed an essential clue that might have led us to Schräge Musik.
On November 18, 1943, Sir Arthur Harris started the Battle of
Berlin. This was his last chance to prove the proposition that strategic
bombing could win wars. He announced that the Battle of Berlin would
knock Germany out of the War. In November 1943, Harris’s bomber force
was finally ready to do what it was designed to do: smash Hitler’s
empire by demolishing Berlin. The Battle of Berlin started with a
success, like the first attack on Hamburg on July 24. We attacked Berlin
with 444 bombers, and only 9 were lost. Our losses were small, not
because of WINDOW, but because of clever tactics. Two bomber forces were
out that night, one going to Berlin and one to Mannheim. The German
controllers were confused and sent most of the fighters to Mannheim.
After that first attempt on Berlin, Sir Arthur ordered 15 more
heavy attacks, expecting to destroy that city as thoroughly as he had
destroyed Hamburg. All through the winter of 1943 and ‘44, the bombers
hammered away at Berlin. The weather that winter was worse than usual,
covering the city with cloud for weeks on end. Our photoreconnaissance
planes could bring back no pictures to show how poorly we were doing. As
the attacks went on, the German defenses grew stronger, our losses
heavier, and the “scatter” of the bombs worse. We never raised a
firestorm in Berlin. On March 24, in the last of the 16 attacks, we lost
72 out of 791 bombers, a loss rate of 9 percent, and Sir Arthur
admitted defeat. The battle cost us 492 bombers with more than 3,000
aircrew. For all that, industrial production in Berlin continued to
increase, and the operations of government were never seriously
disrupted.
There were two main reasons why Germany won the Battle of Berlin.
First, the city is more modern and less dense than Hamburg, spread out
over an area as large as London with only half of London’s population;
so it did not burn well. Second, the repeated attacks along the same
routes allowed the German fighters to find the bomber stream earlier and
kill bombers more efficiently.
A week after the final attack on Berlin, we suffered an even more
crushing defeat. We attacked Nuremberg with 795 bombers and lost 94, a
loss rate of almost 12 percent. It was then clear to everybody that such
losses were unsustainable. Sir Arthur reluctantly abandoned his dream
of winning the War by himself. Bomber Command stopped flying so deep
into Germany and spent the summer of 1944 giving tactical support to the
Allied armies that were, by then, invading France.
The history of the 20th century has repeatedly shown that strategic
bombing by itself does not win wars. If Britain had decided in 1936 to
put its main effort into building ships instead of bombers, the invasion
of France might have been possible in 1943 instead of 1944, and the war
in Europe might have ended in 1944 instead of 1945. But in 1943, we had
the bombers, and we did not have the ships, and the problem was to do
the best we could with what we had.
One of our group of young students at the ORS was Sebastian Pease,
known to his friends as Bas. He had joined the ORS only six months
before I had, but by the time I got there, he already knew his way
around and was at home in that alien world. He was the only one of us
who was actually doing what we were all supposed to be doing: helping to
win the War. The rest of us were sitting at Command Headquarters,
depressed and miserable because our losses of aircraft and aircrew were
tremendous and we were unable to do much to help. The Command did not
like it when civilians wandered around operational squadrons collecting
information, so we were mostly confined to our gloomy offices at the
headquarters. But Bas succeeded in breaking out. He spent most of his
time with the squadrons and came back to headquarters only occasionally.
Fifty years later, when he was visiting Princeton (where I spent most
of my life, working as a professor of physics), he told me what he had
been doing.
Bas was able to escape from Command Headquarters because he was the
expert in charge of a precise navigation system called G-H. Only a
small number of bombers were fitted with G-H, because it required
two-way communication with ground stations. These bombers belonged to
two special squadrons, 218 Squadron being one of them. The G-H bombers
were Stirlings, slow and ponderous machines that were due to be replaced
by the smaller and more agile Lancasters. They did not take part in
mass-bombing operations with the rest of the Command but did small,
precise operations on their own with very low losses. Bas spent a lot of
time at 218 Squadron and made sure that the G-H crews knew how to use
their equipment to bomb accurately. He had “a good war,” as we used to
say in those days. The rest of us were having a bad war.
Sometime early in 1944, 218 Squadron stopped bombing and started
training for a highly secret operation called GLIMMER, which Bas helped
to plan, and whose purpose was to divert German attention from the
invasion fleet that was to invade France in June. The operation was
carried out on the night of June 5-6. The G-H bombers flew low, in tight
circles, dropping WINDOW as they moved slowly out over the English
Channel. In conjunction with boats below them that carried specially
designed radar transponders, they appeared to the German radars to be a
fleet of ships. While the real invasion fleet was moving out toward
Normandy, the fake invasion fleet of G-H bombers was moving out toward
the Pas de Calais, 200 miles to the east. The ruse was successful, and
the strong German forces in the Pas de Calais did not move to Normandy
in time to stop the invasion. While Bas was training the crews, he said
nothing about it to his friends at the ORS. We knew only that he was out
at the squadrons doing something useful. Even when GLIMMER was over and
the invasion had succeeded, Bas never spoke about it. My boss, Reuben
Smeed, was a man of considerable wisdom. One day at Bomber Command, he
said, “In this business, you have a choice. Either you get something
done or you get the credit for it, but not both.” Bas’s work was a fine
example of Smeed’s dictum. He made his choice, and he got something
done. In later life he became a famous plasma physicist and ran the
Joint European Torus, the main fusion program of the European Union.
The one time that I did something practically useful for
Bomber Command was in spring 1944, when Smeed sent me to make accurate
measurements of the brightness of the night sky as a function of time,
angle, and altitude. The measurements would be used by our route
planners to minimize the exposure of bombers to the long summer twilight
over Germany. I went to an airfield at the village of Shawbury in
Shropshire and flew for several nights in an old Hudson aircraft,
unheated and unpressurized. The pilot flew back and forth on a
prescribed course at various altitudes, while I took readings of sky
brightness through an open window with an antiquated photometer,
starting soon after sunset and ending when the sun was 18 degrees below
the horizon. I was surprised to find that I could function quite well
without oxygen at 20,000 feet. I shared this job with J. F. Cox, a
Belgian professor who was caught in England when Hitler overran Belgium
in 1940. Cox and I took turns doing the measurements. My flights were
uneventful, but on the last of Cox’s flights, both of the Hudson’s
engines failed, and the pilot decided to bail out. Cox also bailed out
and came to earth still carrying the photometer. He broke an ankle but
saved the device. In later years, he became rector of the Free
University in Brussels.
After the War, Smeed worked for the British government on road
traffic problems and then taught at University College London, where he
was the first professor of traffic studies. He applied the methods of
operational research to traffic problems all over the world and designed
intelligent traffic-light control systems to optimize the flow of
traffic through cities. Smeed had a fatalistic view of traffic flow. He
said that the average speed of traffic in central London would always be
nine miles per hour, because that is the minimum speed that people will
tolerate. Intelligent use of traffic lights might increase the number
of cars on the roads but would not increase their speed. As soon as the
traffic flowed faster, more drivers would come to slow it down.
Smeed also had a fatalistic view of traffic accidents. He collected
statistics on traffic deaths from many countries, all the way back to
the invention of the automobile. He found that under an enormous range
of conditions, the number of deaths in a country per year is given by a
simple formula: number of deaths equals .0003 times the two-thirds power
of the number of people times the one-third power of the number of
cars. This formula is known as Smeed’s Law. He published it in 1949, and
it is still valid 57 years later. It is, of course, not exact, but it
holds within a factor of two for almost all countries at almost all
times. It is remarkable that the number of deaths does not depend
strongly on the size of the country, the quality of the roads, the rules
and regulations governing traffic, or the safety equipment installed in
cars. Smeed interpreted his law as a law of human nature. The number of
deaths is determined mainly by psychological factors that are
independent of material circumstances. People will drive recklessly
until the number of deaths reaches the maximum they can tolerate. When
the number exceeds that limit, they drive more carefully. Smeed’s Law
merely defines the number of deaths that we find psychologically
tolerable.
The last year of the War was quiet at ORS Bomber Command. We knew
that the War was coming to an end and that nothing we could do would
make much difference. With or without our help, Bomber Command was doing
better. In the fall of 1944, when the Germans were driven out of
France, it finally became possible for our bombers to make accurate and
devastating night attacks on German oil refineries and
synthetic-oil-production plants. We had long known these targets to be
crucial to Germany’s war economy, but we had never been able to attack
them effectively. That changed for two reasons. First, the loss of
France made the German fighter defenses much less effective. Second, a
new method of organizing attacks was invented by 5 Group, the most
independent of the Bomber Command groups. The method originated with 617
Squadron, one of the 5 Group squadrons, which carried out the famous
attack on the Ruhr dams in March 1943. The good idea, as usually happens
in large organizations, percolated up from the bottom rather than
trickling down from the top. The approach called for a “master bomber”
who would fly a Mosquito at low altitude over a target, directing the
attack by radio in plain language. The master bomber would first mark
the target accurately with target indicator flares and then tell the
heavy bombers overhead precisely where to aim. A deputy master bomber in
another Mosquito was ready to take over in case the first one was shot
down. Five Group carried out many such precision attacks with great
success and low losses, while the other groups flew to other places and
distracted the fighter defenses. In the last winter of the War, the
German army and air force finally began to run out of oil. Bomber
Command could justly claim to have helped the Allied armies who were
fighting their way into Germany from east and west.
While the attacks on oil plants were helping to win the War, Sir
Arthur continued to order major attacks on cities, including the attack
on Dresden on the night of February 13, 1945. The Dresden attack became
famous because it caused a firestorm and killed a large number of
civilians, many of them refugees fleeing from the Russian armies that
were overrunning Pomerania and Silesia. It caused some people in Britain
to question the morality of continuing the wholesale slaughter of
civilian populations when the War was almost over. Some of us were
sickened by Sir Arthur’s unrelenting ferocity. But our feelings of
revulsion after the Dresden attack were not widely shared. The British
public at that time still had bitter memories of World War I, when
German armies brought untold misery and destruction to other people’s
countries, but German civilians never suffered the horrors of war in
their own homes. The British mostly supported Sir Arthur’s ruthless
bombing of cities, not because they believed that it was militarily
necessary, but because they felt it was teaching German civilians a good
lesson. This time, the German civilians were finally feeling the pain
of war on their own skins.
I remember arguing about the morality of city bombing with the wife
of a senior air force officer, after we heard the results of the
Dresden attack. She was a well-educated and intelligent woman who worked
part-time for the ORS. I asked her whether she really believed that it
was right to kill German women and babies in large numbers at that late
stage of the War. She answered, “Oh yes. It is good to kill the babies
especially. I am not thinking of this war but of the next one, 20 years
from now. The next time the Germans start a war and we have to fight
them, those babies will be the soldiers.” After fighting Germans for ten
years, four in the first war and six in the second, we had become
almost as bloody-minded as Sir Arthur.
At last, at the end of April 1945, the order went out to the
squadrons to stop offensive operations. Then the order went out to fill
the bomb bays of our bombers with food packages to be delivered to the
starving population of the Netherlands. I happened to be at one of the 3
Group bases at the time and watched the crews happily taking off on
their last mission of the War, not to kill people but to feed them. Freeman Dyson was for many years professor of physics at the
Institute for Advanced Study in Princeton. He is famous for his
contributions to mathematical physics, particularly for his work on
quantum electrodynamics. He was awarded the Lorentz Medal in 1966 and
the Max Planck Medal in 1969, both for his contributions to modern
physics. In 2000, he was awarded the Templeton Prize for Progress in
Religion.
https://sysprogs.com/w/how-we-turned-8-popular-stm32-boards-into-powerful-logic-analyzers/ How We Turned 8 Popular STM32 Boards into Powerful Logic Analyzers March 23, 2017 Ivan Shcherbakov The idea of making a “soft logic analyzer” that will run on top of popular prototyping boards has been crossing my mind since we first got acquainted with the STM32 Discovery and Nucleo boards. The STM32 GPIO is blazingly fast and the built-in DMA controller looks powerful enough to handle high bandwidths. So having that in mind, we spent several months perfecting both software and firmware side and here is what we got in the end. Capturing the signals The main challenge when using a microcontroller like STM32 as a core of a logic analyzer is dealing with sampling irregularities. Unlike FPGA-based analyzers, the microcontroller has to share the same resources to load instructions from memory, read/write th...
http://robotsquare.com/2013/11/25/difference-between-ev3-home-edition-and-education-ev3/ This article covers the difference between the LEGO MINDSTORMS EV3 Home Edition and LEGO MINDSTORMS Education EV3 products. Other articles in the ‘difference between’ series: * The difference and compatibility between EV3 and NXT ( link ) * The difference between NXT Home Edition and NXT Education products ( link ) One robotics platform, two targets The LEGO MINDSTORMS EV3 robotics platform has been developed for two different target audiences. We have home users (children and hobbyists) and educational users (students and teachers). LEGO has designed a base set for each group, as well as several add on sets. There isn’t a clear line between home users and educational users, though. It’s fine to use the Education set at home, and it’s fine to use the Home Edition set at school. This article aims to clarify the differences between the two product lines so you can decide which...
https://theconversation.com/lets-ban-powerpoint-in-lectures-it-makes-students-more-stupid-and-professors-more-boring-36183 Reading bullet points off a screen doesn't teach anyone anything. Author Bent Meier Sørensen Professor in Philosophy and Business at Copenhagen Business School Disclosure Statement Bent Meier Sørensen does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations. The Conversation is funded by CSIRO, Melbourne, Monash, RMIT, UTS, UWA, ACU, ANU, ASB, Baker IDI, Canberra, CDU, Curtin, Deakin, ECU, Flinders, Griffith, the Harry Perkins Institute, JCU, La Trobe, Massey, Murdoch, Newcastle, UQ, QUT, SAHMRI, Swinburne, Sydney, UNDA, UNE, UniSA, UNSW, USC, USQ, UTAS, UWS, VU and Wollongong. ...
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