New boat, U-94.....
After 5 patrols out of St. Nazaire, put in for a transfer to La Spezia. Approved! (went through the null rejection and alt tab out of the game routine on the fourth patrol)
Had all kinds of plans to navigate the Strait, when low and behold... they put my crew and I on a train and shipped U-94 to La Spezia via Fed EX to the new port!
Not very realistic, but hey!
Also, it dawned on me why the boat wouldn't hold it's depth after crash diving and non-combat testing proved it. Crash diving to 210m without a command for silent running showed a loss of compressed air. While silent running, the CE isn't able to get rid of the excess ballast needed to dive so fast. So, if you go silent running before he's able to blow it out you're going down. Simple as that.