Marine Corps snipers struck fear in the hearts of their enemies in the jungles of Vietnam. The exploits of three sharpshooters, in particular, are legendary.

Charles “Chuck” Mawhinney, Eric England, and Carlos Hathcock combined had almost 300 confirmed kills and even more unconfirmed. They were masters of their craft. Their skills in battle, as well as their silent professionalism and humility, made these men examples for the Marine snipers that followed.

“The Marines who go forward and work to put 120 percent into it and let their accolades speak for themselves are the guys that we encourage [Marine snipers] to emulate,” Staff Sgt. Joshua Coulter, a Marine Corps Scout Sniper instructor, recently told Insider.

As skilled marksmen capable of putting precision fire down range at a distance, snipers excel at providing overwatch and gathering intelligence, eliminating enemy officers, and demoralizing opposing forces, among other things.

In many conflicts throughout U.S. history, Marine Corps snipers had proven to be valuable assets on the battlefield. But when the fighting finished, the Corps, time and time again, would fail to build the kind of lasting programs needed to preserve the skills. That finally changed with the Vietnam War.

“Vietnam was the foundation for our modern program,” Coulter said. He explained that the remarkable capabilities demonstrated by Marines like Mawhinney, England, and Hathcock during the conflict highlighted the value of snipers in a very visible way.

“The only reason there is still a sniper program today is the guys who came before us, the quiet professionals who worked their assess off, went down range, and came home,” Coulter said.

They didn’t try to tack their names into the legends of the Corps, but by giving it their all, these snipers left their mark on history.