Free Breathing

Since the B-29 had been "compromised" (i.e., one or more of them had fallen into enemy hands), the Army could reveal further details of the Superfortress' intricate construction. One of these details was the "pressurized" cabin.

When a military plane is six miles up, the crewmen are usually hampered by cumbersome clothing, by oxygen masks which fasten to stationary valves. Not so in the B29. It has a cabin which provides air near sea-level pressure at the highest ceiling.

The principle is not new. Years ago the Army experimented with air pumped into a sealed cabin from a supercharger; the idea was used commercially in Boeing's Stratoliner. But until the B-29s attacked Japan, no pressurized cabins had been exposed by the U.S. to enemy fire.

In tests, experimenters first punctured the airtight fuselage of the B-29 with shells of various sizes. They found that bullet holes did not let out enough air to affect the work of the powerful cabin superchargers (of which the B-29 has two). Even a larger shell hit could be patched before all the cabin pressure was lost. But there was still the danger of a large gaping rent such as a direct ack-ack hit might cause: how would men be affected by the sudden change of pressure?

Big Test. An ex-professor, Major Henry M. Sweeney, found the answer to that one the hard way. He sat down in a pressurized cabin which in turn was within a low-pressure chamber. A hole was punctured in the cabin, the air whooshed from the major's lungs. He was not seriously affected. Apparently close to collapse, he was still able to put on an oxygen mask and pull himself together.

Operation. The pressurized cabin of the B-29 is deflated during a bombing run. The crews plug in cords to their heated suits, don oxygen masks (the B-29 has, besides fixed valves, portable oxygen bottles to be carried when a man moves around, others which can be attached to the parachutes). This is done so that the crew can concentrate on the bombing job without having to worry about oxygen if the plane should be hit.

But after the run the plane is pressurized again by opening an intake valve. The men can then doff their masks and heavy clothes, fly home in comfort.

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