The travel stroke is rarely taught outside the military, but is a useful skill to have. It is a variation of the side stroke that was developed by and taught to the United States Navy SEALs, who call it the Combat Swimmer Stroke (CSS).
When you find yourself in water with a lot of distance to cover, the travel stroke will serve you well, especially when wearing fins. You will tire less quickly if you learn to perform this stroke properly.
The travel stroke allows you to swim more efficiently and reduce your body's profile in the water. It can be used with or without swim fins (flippers). The only difference being that when wearing swim fins your legs always kick in the regular flutter kick motion without the scissor kick.
The object to the travel stroke is efficiency.
You should try to get across a 25m pool in as few strokes as possible.
If you are doing more than 10 strokes per length you are working too hard.
In fact, the fastest and best swimmers get across a 25m pool in 3-5 strokes.
In a big squat position against the wall, push off and stay as streamlined as possible as you glide at least 5-10 meters off the wall. Place your hands on top of each other, place your biceps on your ears, and lock out your arms, streamlined positioning like a rocket.
With a big double arm pull, add the other 3-5 yards to your glide by pulling with your back, biceps and pushing water with your arms using your triceps.
After the arm pull, it is time to breathe, twist and breath then start using the top arm pull as shown. Notice both arms recover together forward, but the top arm pulls from overhead all the way to your hips (similar to freestyle stroke). Then the bottom arm pulls a half stroke (similar to breast stroke) and both arms recover together. Breathe as the top arm completes its pull and the bottom arm begins its pull.
Use the scissor kick and time your kicks so your top leg always goes forward (no matter what side you are on).
You should kick just after both arms have pulled and are recovering, adding more glide to each stroke.
The Travel Stroke is a relaxing and super efficient swim stroke that is an updated version of the traditional sidestroke and a mix of freestyle, breaststroke, and sidestroke:
Start with your body flat and arms in a fully extended position in the water, head pointing down, legs flutter kicking.
One arm then pulls down in the water to the side of the body at the same time rotating the body and the head taking a breath to its side.
The second arm then pulls down with the arm to the side of the body, and the head will move back facing the bottom of the pool, enabling the body to stay horizontal in the water.
The hands move forward fully extended in front of the head
while simultaneously performing a scissor kicking motion cork-screwing the body back to being flat in the water.