First up it's the Imperial Dominion Royal Engineers Dive Suit! Based on early 1900's undersea diving suits, it comes with prim boots, gloves, bodysuit attachments, air tank, and a scripted helmet that will keep your head in place as long as you're wearing it, so it shouldn't be poking out at odd angles when you're looking around, flying, or tumbling down an underwater hill with poor footing.
Also, the helmet is scripted with an air bubble particle effect that only appears when you're underwater! (Rather, under the sim water line.)
All of this for only L$800, and as always, everything is copy/mod/no-transfer!
You can find the Dominion Royal Engineers Dive Suit at any Happy Bivouac location, including the main store in Koreshan:
http://slurl.com/secondlife/Koreshan/155/25/26/?title=The%20Winter%20Assault%20Begins