Jeff,
The mile swim is done a 25 yard pool, in flight suit only, though I would recommend wearing a tee shirt under the flight suit to save on getting rubbed raw by the flight suit on the swim. It is your choice of strokes (I swam the whole thing sidestroke), just so long as you don't touch the bottom or sides of the pool.
They rig a line down the middle of a pool lane, with big orange bouys at each end you swim around, and down the other side. When I swam it, I recall that there were 5-6 people in my lane, and I ended up passing a number of people over and over again.
It really is just a boring time, some people that are weak swimmers have a hard time at it, especially with the extra drag of the flight suit, but I honestly don't recall any of the people in my class that failed the swim.
There are several other "swims" were they evaluate your swimming strokes (yes you are in just a bathing suit, don't recall anyone in my class using goggles, but don't think there was anything against using them), where you swim the first leg free style, then back stroke, then side stroke and finally breast stroke (maybe in a different order, but that basically sums it up). And the swim Nazis blow their whistle at you if they think you are doing the strokes incorrectly.
You also have to tread water (timed), and swim proficiently with all the gear on (flight suit, helmet, boots, gloves, and vest). And you also have to pass jumping off the tower (10 feet max, don't know the exact height) into the water and then swim ~15yards under water. When you come up for air splashing the surface to get rid of simulated oil/fire debris, and going right back down to finish the swim to the other side, a piece of cake!
That is all I can recall, basically the swimming and PT during API was a nice break from the classes, and we either played Volleyball or did some TAE BO (SP?), so it wasn't too bad. The swimming was just to evaluate everyone and supposedly build you up for the final evaluation, so people did get put on remedial swimming at night, but they passed the final test.
Hope that answers your questions,