I was in SEAL Team 20 years ago. Don’t know what it’s like now but the official BUD/s (training) swim was side stroke with dive fins. We only did one open water side stroke wihout fins swim in the first few weeks of training. After that, we used fins. Once you are in SEAL Team, you can use whatever stroke you want for the conditioning swims. The good swimmers swam freestyle. The lazy slobs rolled over on their back and kicked. Side stroke is used in training because the only time you surface swim is when you are doing a beach recon (the old UDT mission). 99% of the swimming I did was underwater compas swims with a drager. We never had to swim like the guy in that video for any operation.