Hi AOI,
Nice decision, but U need to weigh a lot of things before taking a leap.
My suggestion: Since you currently have a good job, I would advice that you take up Masters in Subsea Engineering by distance learning 4 2 yrs (Check out University of Aberdeen & Heriot Watt).
You might find relevant areas of application from your current job. In two years time, you will have earned the MSc. You can even request for a move to subsea operations in your current company. But i would not advise you leave your current job because you wanna pursue the subsea thing. It might not be very easy getting a job, due to your previous experience.
Also, if you can get a study leave from your company, then go for contact learning (1 year) you might be assured of a place wen U come back (either in Desktop support or Subsea opns).
My 2 cents.