Specific to NSI I recommend you use the google and FB searches and will find details.
Honestly though - forget about NSI but think about practical needs. Overall I would share what I think is the obvious - that people entering the Navy should get comfortable with water- entering from a height, the ability to swim several laps, the ability to retrieve 2 bricks from a depth of 10 feet like in Point Break, the ability to get in and out of an inflatable from water, the ability to buddy-drag a peer across the pool, the ability to tread water, the ability to enter clothed and swim, and to disrobe and use clothing as flotation devices, the ability to demonstrate the caddy synchronized swim sequence from Caddyshack (smile) - really just think about what someone might need should the vessel they are on becomes a risk area and they have to enter the drink, help others, help themselves. My DS was on the swim team and if it helps I will share a lot of people in navy training he's attended or on-campus swims so far were not elite swimmers / did not have good stroke form etc but it wasn't a concern as long as they could get from A to B reasonably and were functionally comfortable in the water.
For fun - from A Few Good Men...
Kaffee:
Whoa. Hold it. We gotta take a boat?
Barnes:
Yes, sir. To get to the other side of the bay.
Kaffee:
Nobody said anything about a boat.
Barnes:
Is there a problem, sir?
Kaffee:
No, no problem. I'm just not that crazy about boats, that's all.
Galloway:
J*s*s Chr*st, Kaffee, you're in the Navy for crying out loud.