It's not just a "school".
You will go to boot camp where you will be paid E3, be enlisted at E3, but referred to as an E1 (Seaman Recruit).
Once you graduate, you will be both referred to as a Seaman/Fireman at the rank of E3 but you will also be getting paid the same.
You will then attend 3-6 months of A School Training at E3 pay, and upon graduation you will be automatically promoted to E4 (pay and rank). Almost everybody in Nuclear Power School is an E4 (Petty Officer 3rd Class).
Upon graduation of Nuclear Power School, the first portion of your Enlistment bonus will be paid to you (I think they give you 1/3 your bonus after Power School) and you will move on to Prototype for another 6 months.
At the end of Prototype, you will get the rest of your bonus, all your back sub-pay if you volunteered for the Sub Fleet (comes up to around $1,000 extra) and will begin to collect pro-pay as well, also including sea-pay assuming you move on to the fleet.
