Intention: Swim your 100's or 200's with a little rest in between at a strong but comfortable pace to really push how far you can swim at a good pace.
To set your interval time, time your first 100 or 200 Freestyle and add 15sec to it. So for example if you swim your 100 Freestyle in a 1:50, you will be leaving on the 2:05.
Advanced
Warm up: 400 Choice
4 x 50 (25 Scull / 25 Freestyle) - 10sec rest
4 x 50 Freestyle (count your strokes / -2 strokes each 50) - 10sec rest