Kurt:

Remember that the so-called "high prressure air" is no longer at high pressure once
it enters the tank to be blown; it drops considerably due to normal expansion....

"I think what J.T., Scott and........."

If you blow it dry, as you said, then a lot of hi-pressure air is expended. The WW II
fleet boat I rode, (the USS PIPER (SS-409) normally cruised with Negative tank about 50% of its capacity, (8,000#). In some boats only about 1,500# remained in Negative tank after a blow.) This was an added advantage when it was necessary to surface in an emergency. Bow Buoyancy, Safety and Negative tanks were blown using 3,000# air. Bow Buoyany tank would be blown first, to get an up angle, then Safety tank, which is located amidships, followed by Negative tank.

2nd paragraph: "High internal pressure was not desirable........"

One of the first operations that is accomplished upon nearing the surface, is to
start an air charge. It won't take long to reduce that internal pressure with two
high-pressure air compressors on line.

The Conning Tower on a WW II fleet boat was a separate full-submergence-
pressure compartment situated above the Control Room, which had a lower and upper hatch. The upper hatch was higher than the topside "main deck." The helmsman's station was located there for normal steering mode. If there was a risk of seawater entry before the upper hatch was opened, the lower hatch (which seated with sea pressure) would remain dogged shut, until the 10# low-pressure blower brought the boat to a surface trim, and the upper hatch opened. Depending
on the situation, of course, the upper hatch opening was controlled by th CO, XO or
the diving officer in the conning tower.

I rode Fleet Boats for 10 years, and a Boomer for two years. I spent my first 12 years trying to get on a boat, no matter what type.

Later,

ROBERT M.