America's amphibious Marine Corps and Navy SEALs are some of the most elite fighting forces on the planet, with the ability to deploy in all environments — especially the sea.
That's why the military has created schools to prepare operators from all the sister-service branches to be physically fit, mentally tough, and responsive in high-stress aquatic situations.
During combat water-survival exercises, candidates swim with their hands and feet bound, assemble machine guns underwater, and take on the seas in full combat gear.
Below, we've collected 17 pictures showing just how rigorous their training can be.
A Marine uses his Supplemental Emergency Breathing Device prior to escaping the simulated helicopter seat during Shallow Water Egress Training at the Camp Hansen pool.
Marines and sailors with 2nd Reconnaissance Battalion perform flutter kicks during combat water-survival training at Camp Lejeune, North Carolina.
Petty Officers 3rd Class Brandon McKenney and Randall Carlson assemble an M240G machine gun 15 feet underwater during the 4th Annual Recon Challenge at Marine Corps Base Camp Pendleton.
A sailor performs underwater kettle-bell walks to increase lung power and endurance at Scott Pool, Joint Base Pearl Harbor-Hickam.
Sgt. William Wickett performs a rescue drill during the Marine Corps Instructor of Water Survival Course at Marine Corps Base Camp Johnson, North Carolina.
Basic Underwater Demolition/SEAL students participate in night gear exchange during the second phase of training at Naval Amphibious Base Coronado.
Army candidates tread water during the Combat Water Survival Test, on January 28, 2016.
US Army Master Sgt. Joe Medrano watches as a cadet launches blindfolded and carrying an M16 from a 16-foot diving board during the Combat Water Survival Test, January 28, 2016.
Reconnaissance Marines enter the water with their ankles and hands bound during the water training at Camp Schwab.
A Marine with Combat Logistics Battalion 2, dives underwater to perform a self-rescue drill during a swim-qualification course aboard Camp Lejeune, North Carolina.
Raid Force Marines climb aboard a rigid-hull inflatable boat after conducting combat-swimming exercises at sea.
Mass Communication Specialist 3rd Class Jumar Balacy, right, documents a surface-supplied dive.
Students at the Search and Rescue Swimmer School at Naval Base San Diego rescue a simulated helicopter-crash survivor under the supervision of an instructor.
Sailors conduct cast and recovery training.
An instructor watches as a sailor familiarizes himself with diving equipment while underwater.
A soldier with the Japan Ground Self-Defense Force conducts helo-cast training with 1st Reconnaissance Battalion during Exercise Iron Fist 2014 at Camp Pendleton.
A Marine swims 50 meters (164 feet) with a full combat load during Marine Corps Water Survival Training at the Marine Corps Base Camp Lejeune, North Carolina.
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