I have a pretty standard set of precedures that see me through:
1. Take the shots I've going to take within 2 minutes of game time (sometimes you have more time before destroyers are coming for you, in later years, usually not). If any escort is bow on to you and making speed in your direction, start your dive. Every moment you delay increases the odds of you taking hits during your dive, which will impeded the successful conclusion of this procedure, and your life.
2. Run at
flank speed and emergency dive (tanks flooded) to 120+ metres. Do not worry about silence at this stage, especially if they have any inkling as to your location. If they know where you are, they know where you are, so no sense in being quiet.
3.
When arrived (not while still approaching) at designated 120 +depth, set to "ahead slow and rig for silent running."
Do NOT set silent running before arriving at your designated depth, as (in my experience) you will continue past your intended depth and then past your crush depth, despite all efforts short of turning off silent running. I believe this is due to the silent running command preventing the pumping of excess water ballast from your emergency dive procedure. In short, arrive at your 120+ depth first so your diving officer can adjust ballast with pumps, then set silent running which shuts down the ballast pumps.
4. Immediately after setting ahead slow and silent running, but while still having 6-7 knots of momentum speed from your high speed dive, change direction by 30+ degrees and creep away unmollested. (Depth charges may drop in your neighborhood on their first couple of runs, but they don't really know where you are once going silent, and every run they make, you are farther away each time).
This method, if successfully completed, gets me away 99.9% of the time from 1939 - 1943. It might work in '44-'45 as well, except that you are less likely to be able to complete the steps before being impeded in the manners noted below:
Impedaments to this procedure:
1. You had existing damage, or take damage before reaching 120+ metres, that prevents you from taking your boat that deep and living to tell about it (ie: you crush due to structural damage before or after arriving at 120+ metres)
2. You take a lucky hit (from the DD's perspective) in the first run or two while you are still in the immediate area of where the DD's last heard you. This hit either kills you, forces you to come shallower (flooding, structural damage) which sets you up for further hits, or forces you to increase spead to maintain depth control when flooding), which also allows them to hear you again and make successful follow on attacks.
3. You made your attack from a position with less water depth than your ordered dive, or less than 120 metres depthc in total, and had to level out shallower, or hit the bottom rather than leveling out (done this a few times
). "The captain ordered EMERGENCY DIVE TO 130 METRES! Unfortunatley, the water depth was only 50 metres. The first noise we heard was us hitting the bottom at high speed. The second noise we heard was the sound of hull scraping and flooding. The third noise was the sound of depth charges exploding all around and over our extremely noisy, shallowly bottomed and already flooding boat. We did not live to hear a fourth noise....)