B-29 Discovery of the Jet Stream

MISSIONS WERE SENT OUT WITHOUT EVEN MODERATELY ACCURATE FORECASTS OF WEATHER OVER THE TARGET

We had been told soon after our arrival overseas that weather was a primary factor in limiting operations against the Empire. Most weather over Japan moved down from the permanent high pressure center in Siberia. That meant that the U.S. had no observer stations where reports could be made of the weather approaching Japan. Consequently, missions were sent out without even moderately accurate forecasts of weather over the target – not a desirable way to run a war.

In actuality, it turned out much worse than that suggests, for the conditions encountered at high altitude over Japan came as a real shock. In the first place, the weather was unexpectedly bad during winter months, with layer after layer of cloud formations often piled one on top of another to 30,000 feet or higher. But it was the wind velocities that really astounded the experts. When B-29s began flying high-altitude missions over Japan, Air Force meteorologists realized that the winds aloft were quite unlike anything known before.

The B-29 was designed for high-altitude precision bombing, which required going over a target at 15,000 to 30,000 feet. The wind speeds encountered over Japan at the higher bombing altitudes were regularly 100 to 250 miles an hour and were found on occasion to be more than 300 miles an hour. That meant either going downwind at such a terrific ground speed that precision might be sacrificed – the bombardier would hardly have time to make any corrections after finding the target in the bomb sight – or going upwind and being practically a sitting duck for flak.

IT WAS THE BOMBING OF JAPAN THAT FIRST BROUGHT THE EXISTENCE OF A HIGH ALTITUDE “JET STREAM” TO NOTICE.

We were told that, on one of the first missions flown by the 73rd Wing, the planes swung out east of Japan and then west or northwest toward the target in Tokyo while still climbing to bombing altitude. They were headed more or less directly into the wind, which kept increasing in velocity as they gained altitude. The coastline appeared on the radar scope, inched slightly toward them, hung still for a moment, and then gradually receded. They literally had a negative ground speed. True airspeed at their altitude must have been at least 250 miles an hour and probably 300, but the wind speed was greater.

Before long, Bomber Command was sending weather flights to the Empire almost all the time. Observations made by those flights were the primary source for the all-important forecasts of weather at the targets. It was interesting that those flights – a B-29 flying all by itself over Japan – were rarely attacked by the Japs.