[speed150mph]

Sounds like shrimp, surface and fish so your crew can have shrimp cocktails.

As for the periscope depth, as someone else mentioned, you have to keep your speed at 5 knots or higher, at least you do in the akula, I don't play American subs much. The realistic reason behind this is besides initial diving and surfacing subs are kept at neutral buoyancy and depth control handled by the diving planes. Just as with a planes wings, you need water flow over the planes for them to work. When you try changing depth while stopped it's done using trim tanks and isn't very controlled, resulting in depth fluctuations. Not a bug, just realism at it's best