Question on "wolfpack"

[Platapus]

Citation: Williamson, G (2005) Wolf Pack: The story of the U-boat in World War II. Osprey Publishing Ltd

I am currently re-reading this book. While it is interesting, it does have some historical and technological errors. Some of which are dumb errors. Mr. Williamson is no Clay Blair that's for sure.

There is one particular passage in his book that sounded so blatantly wrong that I questioned my own judgement. Perhaps what he wrote "was" possible?

I never eliminate the hypothesis that I don't know something.

Specifically the passage at the bottom of page 183

Having found a likely target, the commander would bring the bat to periscope depth and, using the navigation periscope, would check that the area was safe and also that the sky above was clear. The boat would then surface, venting the diesel exhaust into the dive tanks to help the boat to surface quickly and also save precious compressed air.

This does not seem possible to me.

I am more familiar with the Type VII design so I can only speak to that.

1. In looking at the technical drawings, there does not seem to be any way to vent diesel exhaust into the dive tanks

2. I don't know why one would want to vent dirty corrosive exhaust into the dive tanks.

3. There is a big difference between compressed air (hundreds of PSI) and exhaust gases from an engine. Venting exhaust gases into a dive tank would not be able to push out the water better than using compressed air.

4. Most importantly, if the boat was in the process of surfacing, the diesel engines would not be operating hence no exhaust gases to vent in to the tanks.. even if possible.

Am I misunderstanding something here?