Dwayne Day has an interesting history comparing undersea exploration technology with space exploration technology.

One other point of coming convergence–the increasing use of underwater suit concepts for space suits (particularly for high-pressure suits that can eliminate the need to prebreathe). Historically, NASA has generally ignored the undersea folks, though there has been a lot of private interaction (Phil Nuytten of Can-Dive has been developing hard suit concepts for decades). It looked like that might be changing with the selection of Oceaneering for the new EMU program, until NASA cancelled the contract and reopened the competition. We’ll see what the future holds, and if Hamilton Sunstrand retains their grip on the agency space-suit budget.