Comments by "vk2ig" (@vk2ig) on "Arctic Ghost Planes" video.

@hshs5756 Other commentators are saying it was the "Put Put", which is called an APU. The APU in the B-29 resides in the rear of the aircraft, just forward of the tail gun position. It is started on the ground prior to engine start by the tail gunner. Once the engineer has started all the engines, the tail gunner shuts the APU down before take-off. This is all described in at least one WW2 era training film for B-29 flight engineers on YouTube.
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