With the beginning of summer, pools all over the U.S. have opened up for recreational swimming — but in the U.S. Navy, recruits are getting ready for the brutal Basic Underwater Demolition/SEAL (BUD/S) training that will turn some of them into Navy SEALs.

In the SEALs, where recruits to the elite special operations unit are pushed to their absolute limits, there can be no room for inefficiency, thusly they developed their own, more efficient swimming stroke, the combat swimmer stroke.

The stroke combines the best elements of breast stroke, and freestyle to streamline a motion that not only reduces resistance on a swimmers body, but also makes swimmers harder to spot in the water.

Unlike freestyle, the combat sidestroke calls for the swimmer to stay completely submerged for the majority of the stroke.

To do the combat swimmer stroke, dive in or kick off as you would in freestyle, but at the end of your glide, execute a large horizontal scissor kick instead. Now comes the unique part — as the horizontal scissor kick tilts your body so one arm is slightly higher than the other, pull that arm back while leaving the other outstretched.

Turn your face up towards the surface as you pull that arm down and take a breath while beginning to pull down your other arm. Another scissor kick and then reset your arms. You should not switch your orientation or the order in which you pull back your arms.

Using the combat swimmer's stroke, Navy SEALs can go for miles in grueling training events that push their physical and mental strength.

Here's a step-by-step breakdown:

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