Pfft, you should know how to set dive depth, Mr. "I sunk 115,000 GRT and was arguably the most successful Drumbeat kaleun"!
hee hee hee...just playin with ya.
"P" is also the keyboard shortcut to drive to periscope depth, and "c" is the shortcut for crash dive (engines ahead flank speed, dive to 70 meters) in case you don't want to mess with the dial.