Just out of curiosity i did a test
Sturgeon class at 500 foot depth, 0 knots
emergency blow - submarine was fully surfaced in 2 minutes 0 seconds
use of full rise on ballast and planes only - submarine was fully surfaced in 2 minutes 42 seconds
repeated the test at 500 foot dept, 25 knots
emergency blow - submarine was fully surfaced in 30 seconds
use of full rise on ballast and planes only - submarine was fully surfaced in 34 seconds.
so in a situation where you are running full bore away from torpedoes, blowing ballast doesnt appear to make that much of a difference
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