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The B-29 bomber, used in WWII, was designed as a high altitude bomber, capable of operating from altitudes in excess of 30,000 feet. However, starting with their first missions to Tokyo in Nov 1944, the B-29s encountered a 200+ mph jet stream which made accurate bombing impossible.

After General LeMay arrived in Jan 1945, he reduced their altitude to around 20,000 feet - sometimes as low as 8,000 feet. Because of improved bombing accuracy, higher bomb loads and acceptable losses, the B-29s never returned to 30,000 feet (except for recon and atom bomb missions).

The public perception appears to be that the B-29 could not be used as a high altitude bomber because of the jet stream. (There were other problems, of course, but the jet stream always seems to be singled out as the reason.)

B-29 dropping bombs

The picture above has been described as an illustration of the effect of the jet stream on bombing accuracy. See XXI Bomber Command

My understanding of the jet stream (including the jet stream over the US) is that it is stronger in the winter, fairly localized and often changes speed, altitude and location.

Was it just bad luck that the B-29s encountered the jet stream over Tokyo in the winter of 1944? Could the jet stream have moved or weakened by Mar 1945 - when the low level raids were first conducted? Or is there a persistent high speed jet stream over Tokyo or mainland Japan every winter?

ADDENDUM

Vern Haugland of the AP wrote a lengthy article "World's Most Violent Winds Are Problem in Bombing Tokyo" [Evening Star, Washington, DC (Jan 8, 1945), Page A-2] which described, in great detail, problems caused by the winds encountered over Tokyo and the extreme cold at 30,000 feet.

The article did not use the term "jet stream". That term did not appear until 1949 when scientists published studies describing the discovery of "the jet streams of wind blowing from east to west around the world at different latitudes". [Evening Star, Washington, DC (Apr 20, 1949), p. A-6]

Thus, it is possible that, given their limited knowledge of what was happening, the military did not realize that what they were dealing with could have been a temporary phenomenon.

p.s. The picture above is probably not an illustration of problems caused by the jet stream because both the aircraft and the bombs should be traveling at the same speed within the jet stream. Instead, it could be illustrating the effects of wind shear, where winds at different altitudes are moving at different speeds.

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    $\begingroup$ The most amazing thing about the B-29 was its defensive fire control. The GE system wasn't just guns pointed by remote control. The gunner aimed at the target with a sighting head, but he was just sending voltages via Selsyn synchros to a central electronic analog computer and the computer did all the actual pointing the guns after correcting for all the variables, like parallax error, lead, ballistics etc. So the sight head's alignment and the gun alignment was never the same. 15 years before the concept started to be applied to flight controls, it was a true "fly-by-wire" control system. $\endgroup$
    – John K
    Jun 14 at 14:59
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Jets form along warm/cold airmass boundaries, such as the mid latitude Polar and Tropical air mass borders, where the warm side tapers off into a wedge shape at the top of the airmass at the tropopause. So jets form randomly at different locations along the writhing "belt" of Polar/Tropical frontal boundary that is always present along the mid latitudes around the earth.

It was a bit of bad luck insofar as Japan is at a latitude that places it frequently on the Polar/Tropical airmass boundary if the frontal conditions were right, so jets could frequently form at places that happen to be over a particular target. Jets were only dimly understood and were likely very difficult to predict with the weather technology of 1945. So the bombardier only knew he was in a jet when he was in it.

Surprisingly, jet stream problems notwithstanding, according to this article, bombing accuracy over Asia was roughly the same as Europe, with about a third of bombs hitting within 1000 ft of the aim point on precision raids (but the Norden was supposed to do better than that).

So I suspect that jet streams were an occasional problem (because they come and go), but the larger one was simply the vertical distance that magnified the Norden's error band, which was a problem in Europe and Asia. Also, even without being in a jet, if you imagine the variation of winds through 4 or 5 miles of air, and the fact that the Norden made its ballistic wind drift compensation based on the airplane's track/heading offset at its bombing altitude, it's not hard to see the overall problem, jet or no jet.

In Europe, precision was vastly increased when bombing altitudes were lower to the mid teens in the last 6 months, where the Norden really could place bombs with great accuracy (60% hitting within 1000 feet).

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    $\begingroup$ That's a great article. Only 4 days of visual bombing per month? The B-29 was equipped with radar which they could use to perform "offset" bombing through the clouds - using the coastlines as reference. But the radar operators with the training to do so would not arrive for several months. $\endgroup$ Jun 13 at 4:46
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    $\begingroup$ And useless for going after specific targets like manufacturing plants. It was only good for area bombing. The WWII equivalent to the precision strike was the B-26 or B-25 bombing from 12-14000 ft where the Norden really excelled. They are the ones to took out the very small precision targets like small to medium size marshalling yards, bridges etc. $\endgroup$
    – John K
    Jun 13 at 13:09
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    $\begingroup$ Based on the information you provided, it appears that the jet stream may not have been the primary reason they decided to abandon high altitude bombing - but it provided a convenient excuse. Given that the B-29 and Norden bombsight were the 2nd and 3rd most expensive projects in the War, no one would have wanted to admit that they were not performing as planned. Contemporary newspaper accounts describe the high altitude winds, but not the other issues. $\endgroup$ Jun 14 at 7:55
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    $\begingroup$ I think the 4 day per month thing might refer to bombable days of specific targets, not Japan overall. There is also some popular misinformation about the Norden. Its general workings were well known by the Germans during WWII because it was developed in the 30s before the heavy secrecy was imposed. The gap between expectations and results was because it was demonstrated to the Army from only10000 ft. $\endgroup$
    – John K
    Jun 14 at 12:49
  • $\begingroup$ @JohnK: Why was radar-directed bombing useless for pinpoint targets? Once you know your location relative to the coastline, it seems that it should be easy (at least in theory) to use that plus the known location of the target relative to the coastline to drop bombs on the target from above the clouds. $\endgroup$
    – Vikki
    Sep 5 at 19:14
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The B-29 could carry high explosive or incendiary bombs, or a mixture of both. High explosive bombs have a much higher terminal velocity, there for in the presence of appreciable cross winds, high altitude precision bombing with mixed loads would be nearly impossible.

In a 50 mph cross wind:

HE bomb terminal velocity of 600 mph reaches the ground from 6 miles up in around 40 seconds. The crosswind would move it around 2/3 of a mile.

Incendiary bombs terminal velocity of 300 mph would take 1 minute 20 seconds with a drift of over a mile.

They weren't going to hit anything and General Le May knew it. The decision to go low and carpet bomb with incendiary bombs effectively destroyed most of the major cities, but inflicted massive civilian casualties from the firestorms created.

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  • $\begingroup$ Yes, the incendiary bombs were not streamlined for high altitude. The plan was apparently to drop them at night when it would be safer to bomb from lower altitudes (as the British had done in Europe). The firestorms which occurred at Tokyo, Hamburg and Dresden were not part of the plan. Instead, once again, the weather played the key role in creating them. $\endgroup$ Jun 15 at 17:06
  • $\begingroup$ Sadly, such a beautiful aircraft tasked with such an ignominious role. $\endgroup$ Jun 15 at 17:27
  • $\begingroup$ By that time in the war, area bombing using incendiaries was considered a necessary part of the second objective of the bombing strategy - to demoralize the public. [See "The Effects of Strategic Bombing on Japanese Morale" (June 1947), available online] The B-29 was used in other roles, such as strategic bombing of airfields during the Battle of Okinawa to thwart the Kamikaze threat. One of their most successful roles was with the low-level aerial mining missions. $\endgroup$ Jun 15 at 20:50
  • $\begingroup$ Well, on to better times. The B-50 did offer some excellent improvements, exceeding 400 mph with 2 added jets. $\endgroup$ Jun 15 at 21:54
  • $\begingroup$ @RobertDiGiovanni: The jets were only used on the KB-50 tanker version, and only because it couldn't fly fast enough without them to refuel high-speed jet fighters and bombers. The bomber version of the KB-50 never had them. $\endgroup$
    – Vikki
    Sep 5 at 19:16
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The above picture has been described as an illustration of the effect of the jet stream on bombing accuracy.

If the suggestion is that the physical effect of the wind shear around the jet stream upset the flight path of the bombs enough to be visible in a photo taken at close range-- that is highly unlikely and casts doubt on the credibility of any source making that argument. The jet stream was not the primary obstacle to accurate bombing from high altitudes with the B-29 over Japan.

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  • $\begingroup$ I've added the link to the picture. I would not normally cite a Wikipedia link as an authoritative source. Instead, I would cite their sources. However, this appears to be a case where the author of the Wikipedia article either engaged in a little editorial license or found the picture on a site which had that caption. In either case, the caption is wrong. $\endgroup$ Jun 15 at 16:57

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