I would not use any auto mode.
Why not?
I've recently been chatting with a person who has done underwater photography for a very long time and they use primarily auto mode with an amphibious digital camera. Or maybe it depends on the camera you're using???
Which camera and what lighting setup?
In scene mode on the S90, S95, S100, RAW is not available, only P mode. Then in P mode, you don't always know what shutter and aperture the camera is going to select.
The only way to safely shoot jpeg underwater and get consistent results is to use twin external strobes so that your lighting is guaranteed to be consistent. Otherwise, it is a crap shoot. The OP is using a camera and a case, no strobes were mentioned.
Sure, you can use auto or p mode, but you are effectively cutting off your right arm, or poking your eye out by doing so.
Using auto or P mode limits your possibilities too much.
On land, I only use RAW when I think I might need to PP, I still shoot in JPEG a lot of the time where I am confident about the lighting. But underwater, the conditions are much more challenging and if you shoot jpeg you are likely to lose a lot of your shots due to unrecoverable white balance. The camera's scene mode is simply not up to the job if you want to get a good keeper rate.
In most cases, shooting underwater is a one time only opportunity. On land, that tree or pond or building is always going to be there. But every time you go down, the water conditions, lighting and wildlife are likely to be very different so it makes sense to cover all your bases.
