I'm in the early stages of planning for a diorama based around a submarine breaking the water's surface. Anyone here have any experience with this or can you recommend any good sites on the subject?
Thanks in advance! 
This is a huge topic and something very difficult to do well... there are so many different products and ways of achieving various effects that you could easily write a book on it...and still leave a lot of unanswered questions.
My advice, to anybody doing water, is to first of all VERY clearly define precisely what you want to achieve and it is helpful to sketch it out marking where you need different water effects i.e. ripples. waves, white-water, splashes, wet-surfaces...the reason being that all of those utilise different techniques, and in some cases different products.
There is, with water, a case for getting the right product for the right type of effect; you dont have to, you can get away with single products for all effects, but it often makes the job harder than it need be. A lot of water effects are reliant on building-up layers and being very aptient with settings vicosities to get different effects....Water is HARD to do well and EASY to do wrong.
Jumping into a large diorama without practising first on smaller pieces really sint something I would advise tbph as when water goes wrong it generally ruins the entire piece... So:
Sketch out what you want to do and define the different water effects - then practice achieving each one of those effects on small pieces until you are comfortable doing them - then once comfortable doing all of the effects individually, combine them together on the large diorama/model.
You will realise, in doing those individual techniques, how some methods/effects require set orders of work and how they can interfre, or combine, with each other.
Dropping straight into it, without any practice... in my expereince, usually results in dissapointment.