(CNN) -

"Faithful unto death."

Those words on the West Point headstone of 1st Lt. Alonzo H. Cushing succinctly enshrine the determination of the man who helped turn the tide at Gettysburg during the Civil War.

Despite two severe wounds, Cushing, 22, stayed at his post and directed artillery fire upon hordes of Confederates charging the center of the Union line at Cemetery Ridge -- a doomed assault known as Pickett's Charge. A bullet to the head finally felled the young officer.

More than 151 years after his heroic service, Cushing will receive the Medal of Honor posthumously, the White House announced Tuesday.

The Medal of Honor is the country's highest military award, given to American soldiers who display conspicuous "gallantry above and beyond the call of duty."

The recognition for the West Point graduate marks the longest span of time between the event and the bestowal of the award, said the Congressional Medal of Honor Society.

"He does deserve it without a doubt," said John Heiser, historian at Gettysburg National Military Park. "The tragedy is ... that it should have been awarded long, long ago."

Cushing, born in Delafield, Wisconsin, commanded the six-gun Battery A, 4th U.S. Artillery, at the momentous Pennsylvania battle.

His battery took a pounding from Confederate artillery preceding the attack and he had only two serviceable guns when the charge began on the hot afternoon of July 3, 1863. The estimated 13,000 attackers had what is known as "The Angle" as their objective and some were able to briefly breach the stone wall.

Artillery shell fragments left Cushing with injuries to his left shoulder and groin.

"Refusing to evacuate to the rear despite his severe wounds, he directed the operation of his lone field piece continuing to fire in the face of the enemy," the White House said in a statement. "With the rebels within 100 yards of his position, Cushing was shot and killed during this heroic stand. His actions made it possible for the Union Army to successfully repulse the Confederate assault."

Heiser said that the battery -- which included 126 officers and enlisted men -- had the misfortune of being in the center of the maelstrom on the third day of the pivotal battle.

"His battery was under fire for an hour and a half," Heiser said. "It was left in shambles and destroyed." Six men were killed and 32 were wounded.

Given the status of his wounds and his battery, Cushing had every reason to withdraw, said Heiser.

"He is going to show those Rebels one way or the other that his battery will be in action to the end," said Heiser. "It is upholding the highest level of what the Army says is honorable service."

Katie Lawhon, management assistant at Gettysburg, said visitors today can see where Cushing's battery served.

"The story of his valor and sacrifice at the center of the Union battle line ... is a very inspiring story to a lot of people who study Gettysburg," said Lawhon.

Honor for Cushing is a long time coming

Tuesday's announcement culminates years of lobbying for the honor. Cushing was recommended in 2010, but Congress did not give formal approval until late last year.

Cushing received a waiver of a requirement that the Medal of Honor must be recommended within two years of the event and presented within three years, Laura Jowdy, archivist with the Congressional Medal of Honor Society, said Wednesday.

The recommendation then had to go through the Defense Department and to the White House, where President Barack Obama gave his approval.

Margaret E. Zerwekh, 94, of Delafield, has been an integral part of the campaign, writing to Wisconsin congressmen. She's conducted research, and lives in a house on property formerly owned by the Cushing family.

"He saved the Union and he needs to have recognition for it," Zerwekh said late Tuesday. "It is about time."

Heiser said the heroism of Cushing was "kind of forgotten, shoved to the background." A first sergeant in the battery years later received the Medal of Honor, while several surviving comrades kept alive Cushing's bravery.

The White House did not release a date for the Cushing ceremony.

At a ceremony on Sept. 15, Obama will bestow the Medal of Honor to two soldiers who fought in Vietnam.

Command Sgt. Major Bennie G. Adkins, who lives in Opelika, Alabama, distinguished himself in combat operations in March 1966 during one of three tours in Southeast Asia. He dragged comrades to safety during a mortar barrage and later fought off an attack.

Specialist Four Donald P. Sloat, from Coweta, Oklahoma, was killed while on patrol in January 1970. The 20-year-old machine gunner chose to shield the blast of a grenade with his own body, saving three comrades.