>What is few degrees down bubble?

In other words, don't adjust your sub to sit on an even keel when it's sitting still. Instead, "trim" it--for our dynamic divers, that means adjust the placement of weights and/or foam--so that the front end points down five degrees, maybe ten (where zero degrees would be horizontal...ninety degrees would be a straight down nosedive...so you can figure five or ten degrees is slight).

"Up/Down bubble" refers to angle of the boat (not of the planes, by the way, that's separate ). If I'm not mistaken, in US Navy diving protocol the conn may order "x degrees down" to start a dive or affect the rate of descent. I don't know if it's required or optional, as I think the conn might instead just order "Make your depth xxx feet."

I would think "Make your depth..." would be mandatory, but the degrees-down command would be for starting to dive with depth as yet unspecified.