Combat Sidestroke (CSS)
The combat sidestroke (CSS) is a hybrid swimming technique developed for military applications that combines elements of sidestroke, freestyle, and breaststroke. It is the preferred stroke for the PST 500-yard swim and the primary swimming technique used throughout BUD/S training and NSW operations.
Why CSS Over Other Strokes
The combat sidestroke is designed for efficiency and stealth. It keeps the swimmer's profile low in the water, generates strong propulsion with minimal splash, and allows for easy breathing without lifting the head. In an operational context, these qualities matter for combat swimmers approaching a target. In a training context, CSS is simply the fastest way to cover distance with the least energy expenditure using approved PST strokes.
CSS Technique Overview
CSS combines a scissors kick with a pulling motion similar to freestyle. The swimmer alternates sides to distribute the workload evenly. The top arm performs a recovery similar to freestyle, while the bottom arm pulls through the water. The kick is a modified scissors kick that provides the primary propulsion. Breathing occurs naturally as the head rotates to the side during the recovery phase.
Learning CSS for BUD/S Preparation
Candidates who come from a competitive swimming background may need to retrain their muscle memory for CSS, since it differs significantly from freestyle or backstroke. The key is efficiency — a good CSS swimmer covers distance with fewer strokes and less energy than a breaststroke swimmer. Practicing CSS during every LSD and interval swim session builds the stroke efficiency that translates directly to PST performance and BUD/S pool work.
Film yourself swimming CSS from above and from the side. Most inefficiencies are invisible to the swimmer but obvious on video.
Related Terms
The 500-yard swim is the first event of the Physical Screening Test (PST) and measures a candidate's aquatic endurance. Performed using either the combat sidestroke (CSS) or breaststroke, it tests the sustained swimming capacity required for BUD/S water-based evolutions.
The Physical Screening Test (PST) is the standardized fitness assessment used by Naval Special Warfare to evaluate candidates for SEAL training. It measures performance across five events: 500-yard swim, push-ups, sit-ups, pull-ups, and a 1.5-mile run, each with minimum and competitive score thresholds.
Long Slow Distance (LSD) training is a cardio methodology that emphasizes sustained, moderate-intensity effort over extended durations. In BUD/S preparation, LSD sessions build the aerobic base required for long swims, runs, and the prolonged physical output demanded throughout SEAL selection.
Interval training is a cardio method that alternates between high-intensity work periods and active recovery periods. In the NSW preparation program, interval sessions target running and swimming speed by training the body to sustain faster paces through repeated timed efforts.
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