This method is somewhat similar to "submersion swimming," where the entire body is submerged in water, swimming like a fish.
"Submersion swimming" is not particularly unusual, but it became well known due to the swimming competitions at the Olympic Games.
In the swimming pools of the Olympic Games, if you pay close attention, you'll notice that at the pool bottom, 15 meters from each side of the lane, there is a white line. This line is specifically there to remind swimmers of the maximum distance they can swim submerged before they must surface; otherwise, they will be disqualified by the judges.
The reason for this rule is mainly because normal swimming styles, which involve switching between water and air, create considerable resistance when swimming.
Submersion swimming nicely solves this problem by reducing resistance, naturally increasing speed as a result.
