One Armed Swimming

Every now and then, my swim coach would make us do what he called the “scooter drill”.
You take a pull buoy and hold it one hand in front of you, as you swim with one arm for a set number of strokes. Then you switch hands and swim with the other arm for a number of strokes. It’s sort of like getting on a scooter and pushing constantly with one leg to make it go.
It’s also an annoying drill because no one is used to swimming with one arm generally.
I hated it. As I swam down the 50m length, I would be OK for a few strokes and then I start getting tired, and get slower and slower, until I’m totally wiped out just reaching the other wall.
I grew determined. I wanted to be able to do this drill, which others seemed to do OK and seem to be so fast going down the length of the pool.
During my off season, I started doing intervals of swimming with each arm for 25m. I would successively increase both the number of intervals and the distance I swam with each arm. I eventually reached swimming a 400m with one armed swimming for 200m each. I would then do other shorter intervals for a total of a 1000m set. I would do this 2-3X a week during the off season, and as I entered into the base phase, I would do this once a week while swimming normal workouts the other 2 times.
As expected, my “scooter drill” improved greatly. I got much faster and fatigued a lot less, as I was working out with one arm a lot longer than the scooter drill intervals. But another more amazing thing happened; my regular swimming got a ton stronger and faster.
One big thing I suffered from was that my stroke would kind of fizzle out at the end of the stroke, near my hip as it exitted the water. In doing one arm swimming, I was now able to keep my stroke strong through its entire length, and for longer durations. I could still be strong swimming for workouts up to 4000m. In addition, I was able to lower my stroke rate and thus not be so out of breath and/or wiped out AND my swim speed increased.
One arm swimming really bummed me out. I rallied, took matters into my own hands, and improved my one arm swimming ability in a focused manner. But then I realized the benefits of this strength increase in both endurance and speed.