This is a technique video on swimming about 40m underwater in the pool.
TFR 158 - Are You Ready? Preparation Assessment Tools
Stew Smith (https://www.stewsmithfitness.com) and Jeff Nichols (https://www.performancefirstus.com) discuss some objective grading criteria each use to assess a candidates progress along the journey and training timeline as they prepare for any spec ops selection program.
Article on the topic with charts referenced in the video:
Check out other videos of combat swimmer stroke, workouts, and other spec ops related training. See https://www.stewsmithfitness.com for more information about military, law enforcement, special ops, fire fighting training programs.