Update: This story was corrected to reflect that Byers was a Special Operations Combat Medic.

U.S. Navy Hospital corpsmen are part of a tradition that predates the American Navy itself. In the age of sail, corpsmen (then called loblolly boys) helped the ship's surgeon stay on his feet with sand and kept the cauterizing irons hot. The role has evolved over the decades, and the name of the corpsman's rating evolved along with it. The loblolly boy became the nurse, who became the bayman, who became the surgeon's steward, then the apothecary, hospital apprentice, hospital steward, pharmacist's mate, until after World War II, when the modern corpsman (as we know it) was born.

Petty Officer 3rd Class Heston Johnson, corpsman, Bravo Company, 1st Battalion, 7th Marine Regiment, provides security during a mission in Helmand province, Afghanistan, July 4, 2014. (U.S. Marine Corps photo by Cpl. Joseph Scanlan)

The corpsman is part medic, part nurse, part pharmacist, who serves in the Navy and on its ships, but also deploys with Marines. A corpsman's importance in combat is unrivaled and requires the skill and courage of any grunt. 2,012 corpsmen were killed in action in the history of the U.S., with 42 of those lost in Iraq and Afghanistan. Their work earned the recognition of twenty ships named for them and more than 600 medals for valor, including twenty-two Medals of Honor. Here are the stories of twenty-two of the Navy's bravest:

1. Hospital Apprentice Robert H. Stanley

Stanley volunteered to carry and deliver sensitive messages between the American and British forces while under heavy gunfire during the Boxer Rebellion in Beijing, China.

Photo from Bureau of Medicine and Surgery, Department of the Navy

2. Hospital Apprentice First Class William Zuiderveld

Zuiderveld was known as "Doc" to his company of armed Navy sailors (nicknamed "Bluejackets") during the seizure of Vera Cruz. During an ambush, one of the men was shot in the head and Zuiderveld answered the call for a "corpsman." Rushing to their aid, he purposely exposed himself to enemy fire to reach his wounded comrades.

U.S. Navy photo

3. Hospital Apprentice Fred H. McGuire

During the Philippine Insurrection, McGuire began running low on ammunition, causing him fight off the fierce enemy forces with only his rifle's butt stock until relief arrived. Finally free to treat the wounded, McGuire attended to several Americans who otherwise would have died.

4. Hospital Steward William S. Shacklette

After the deadly boiler explosion on the USS Bennington and suffering from 3rd-degree burns over much of his body, Shacklette risked his life to assist dozens of sailors off the ship and to safety.

U.S. Navy photo

5. Pharmacist's Mate First Class John H. Balch

Fighting alongside his Marines from the 6th Regiment during the Battle of Belleau Wood, Balch exposed himself to high-explosive fire to secure the wounded. He worked tirelessly for his save his patience's lives.

U.S. Navy photo

6 . Hospital Apprentice First Class David E. Hayden

Crossing into a hail of heavy machine-gun fire in an open field during the Battle of Saint-Mihiel, Hayden administered lifesaving treatment to a wounded Marine. Hayden was wounded but saved the Marine's life by carrying the man to safety.

7. Hospital Apprentice First Class Robert Eugene Bush

Stationed with 2nd Battalion, 5th Marines in action against the Japanese on Okinawa, Bush took shrapnel from three enemy grenades. Despite the losing one eye, he was able to do his job and while tending to his wounded platoon commander. While holding the plasma bottle he was giving the Marine officer, he unloaded first his pistol and then the officer's carbine into an oncoming wave of Japanese soldiers. The Japanese retreated and Bush ensured his wounded were evacuated before administering to his own wounds.

8. Pharmacist's Mate 2nd Class William D. Halyburton

Serving in a rifle company with the 5th Marines on Okinawa, Halyburton noticed his company was suddenly pinned down. Moving forward towards the enemy, he reached a wounded Marine and unselfishly shielded the man using his body to shield incoming Japanese gunfire. He continued with his medical treatment until he collapsed from his wounds, sacrificing himself for the wounded Marine.

9. Hospital Apprentice First Class Fred F. Lester

Crawling towards a casualty under a barrage of hostile gunfire and bleeding badly from gunshot wounds, Lester successfully pulled a wounded Marine to safety and instructed two of his squad members how to treat the Marine. Realizing his own wounds were fatal, he instructed two others on how to treat their wounded comrades. Soon after, Lester succumbed to his injuries but saved dozens of lives during his tour.

10. Pharmacist's Mate First Class Francis J. Pierce

Pierce earned his Medal of Honor at the Battle of Iwo Jima. With his rifle blasting, he courageously unveiled himself to draw off enemy attackers while he directed litter teams to carry off wounded Marines towards the medical aid station. He again drew fire while trying to treat a wounded troop and killed another Japanese soldier in the process. He ran across 200 meters of open ground to pick up a wounded Marine and carry him back across the same open 200 meters. Francis rendered the care of several severely wounded men while during the campaign.

11. Pharmacist's Mate Second Class George E. Wahlen

Under the command of 2nd Battalion, 26th Marines at Iwo Jima, Wahlen was positioned adjacent to a platoon that had come under fire and began taking mass casualties. Dashing more than 600 yards to render medical care on fourteen Marines before returning to his platoon unharmed.

12. Pharmacist's Mate Third Class Jack Williams

Under intense enemy fire, Williams dragged a wounded Marine on his hands and knees, using his body to shield the man as managed to apply battle dressings to the wounded. Shot in both the abdomen and groin, Williams was stunned, but unwilling to give up, recovered and completed to treat the wounded Marine before addressing his injuries.

13. Pharmacist's Mate First Class John H. Willis

Injured by shrapnel and refusing to seek medical attention, Willis advanced up to the front lines under heavy mortar and sniper fire where he saved an injured Marine laying in a crater. Willis administered plasma to the patient as the Japanese intensified their attack throwing grenades. Willis returned the frags launching back towards the enemy. After surviving several attempts, one grenade exploded in his hand killing him instantly. The Marine survived.

14. Hospital Corpsman Third Class Edward C. Benfold

Benfold was killed in action in Korea while trying to help two Marines in a crater at the Battle of Bunker Hill. His company was battered by an enemy artillery barrage and the charged by a battalion-sized unit. Benfold ran from position to position to help his injured comrades. When he came upon the two Marines in a crater, he saw two grenades thrown in as two enemy soldiers rushed the position. Benfold picked up the grenades and charged at the two attackers, pushing the grenades into their chests. He was mortally wounded in the subsequent explosion.

15. Hospital Corpsman Third Class William R. Charette

While attending to a wounded man during the Korean War, an enemy grenade landed within a few feet of William, who immediately threw himself on the man, absorbing the blast with his body. Now experiencing extreme shock, he continued to administer medical care to his wounded brother before patching up himself.

16. Hospitalman Richard D. Dewert

As a fire team became pinned down by an overwhelming source of gunfire, Dewert darted into the fray on four different occasions. He carried out the wounded from the front lines even after suffering a gunshot wound to his shoulder. His courageous acts and refusal to quit allowed his brothers to survive their life-threatening injuries.

17. Hospitalman Francis C. Hammond

After sustaining a vicious attack from hostile mortars and artillery by enemy troops, Hammond maneuvered through rough terrain and curtains of gunfire, aiding his Marines along the way. He skillfully directed several medical evacuations for his casualties before a round mortar fire struck within mere feet of him.

Illustration of Francis C. Hammond by Mario A. Demarco. It was part of an issue of the Francis C. Hammond Middle School Newspaper.

18. Hospitalman John E. Kilmer

During the Korean War attack on Bunker Hill, Kilmer suffered from multiple fragment wounds but still traveled from one position to another, tending to the care of the injured. Although he was mortally wounded, he successfully spearheaded many medical evacuations. As mortar shells rained down around him, Kilmer rushed to a critically wounded Marine. Shielding the man from the incoming shrapnel, Kilmer was struck by enemy fire. He's credited with saving many lives.

19. Hospital Corpsman Second Class Donald E. Ballard

Upon returning from rendering care on two heat casualties, his platoon came under a determined ambush from the North Vietnamese Army (NVA). Noticing an injured Marine, Ballard dashed to the man's aid, treating his wounds. He directed four Marines to form a litter team to evacuate the almost dead Marine when he spotted an incoming enemy grenade. Ballard threw himself on the explosive device, protecting his brothers. The grenade failed to detonate. He stood back up and continued the fight, treating the other Marine casualties.

20. Hospital Corpsman Third Class Wayne M. Caron

While patrolling through a rice patty, Caron's squad began taking small arms fire. Seeing his comrades sustain mortal wounds, he raced to each one of them and delivered medical attention to at least four Marines while suffering from two gunshot wounds. The injury didn't stop Caron, he continued onward, putting the well-being of his Marines above his own.

21. Hospital Corpsman Third Class Robert R. Ingram

During an intense battle against dozens of NVA troops, Ingram's platoon began to thin out. Danger close, Petty Officer Ingram crawled across the weathered terrain to reach a downed Marine as a round ripped through his hand. Hearing the desperate calls for a corpsman, Ingram collected himself and gathered ammunition from the dead. As he moved on from patient to patient, he resupplied his squad members as he passed by. Continuing to move forward, Ingram endured several gunshot wounds but continued to aid his wounded brothers. For nearly eight hours, he blocked out severe pain as he pushed forward to save his Marines.

22. Hospital Corpsman Second Class David R. Ray

During the early hours of the morning near Phu Loc 6, a battalion-sized enemy force launched a determined assault against the position Ray's squad occupied. The initial attack caused numerous casualties. Ray moved from parapet to parapet, tending to his wounded Marines. Protecting his own, Ray killed one enemy soldier and wounded a second. Although mortally wounded, he held off the enemy until running out of ammunition. While treating his last patient, Ray jumped on a wounded Marine as a nearby grenade exploded, saving the Marine's life.

23. Senior Chief Special Warfare Operator Edward Byers

Then-Chief Edward Byers was trained as a Special Operations Combat Medic at Fort Bragg, North Carolina, before going through SEAL training in 2002. As part of a hostage rescue force in Afghanistan, he assaulted an enemy sentry while rushing into a small room filled with heavily armed enemy fighters. He assaulted, tackled and fought the insurgents in hand-to-hand combat and then threw himself on the hostage to shield them from small arms fire. While shielding the hostage, Byers subdued others with his bare hands. The 36-year-old is still serving on active duty after 11 deployments. He is the most decorated living Navy SEAL.