Although a Blizzard dubbed Storm Jonas is roaring through the U.S. East Coast, dumping up to two feet of snow on the nation's capital, the soldiers who guard the Tomb of the Unknowns at Arlington National Cemetery remain at their post.

Sentinels of the U.S. Army 3d U.S. Infantry Regiment's "Old Guard" have kept a constant vigil at the Tomb of the Unknown Soldier at Arlington National Cemetery around the clock for nearly a century, through hurricanes, blizzards and deep freezes. The soldiers can find temporary shelter in a guard hut designated as Post One, but they must still stand "at ceremonial at ease" while holding their weapon in front of them, according to one former tomb guard.

The sentinels must leave the guard hut -- Post One -- at least every five minutes "and take a trip up and down the mat" in front of the tomb, a former guard tomb said.

The commander of the relief, who is a sergeant, can shorten the guard's shifts if the cold is too harsh, a former commander tells Lead Stories. The overnight shift is usually for two hours at a time, but that is sometimes reduced to just 30 minutes in bad weather, he said.

The Tomb of the Unknown Soldier is the final resting place for the unidentified remains of three American military personnel killed in the first two world wars and the Korean conflict. A service man killed in Vietnam was interred there in 1984, but exhumed and moved in 1998 after DNA testing confirmed his identity.

From the U.S. Army's website:

The Tomb Guard marches 21 steps down the black mat behind the Tomb, turns, faces east for 21 seconds, turns and faces north for 21 seconds, then takes 21 steps down the mat and repeats the process.

Duty time when not "walking" is spent in the Tomb Guard Quarters below the Memorial Display Room of the Memorial Amphitheater where they study cemetery "knowledge," clean their weapons and help the rest of their relief prepare for the Changing of the Guard.

Sentinels, all volunteers, are considered to be the best of the elite 3rd U.S. Infantry Regiment (The Old Guard), headquartered at Fort Myer, Va.

Each Tomb Guard must be in superb physical condition, possess an unblemished military record and be between 5 feet, 10 inches and 6 feet, 4 inches tall, with a proportionate weight and build. An interview and a two-week trial to determine a volunteer's capability to train as a tomb guard is required.

The Tomb of the Unknown Soldier at Arlington National Cemetery stands atop a hill overlooking Washington, D.C. On March 4, 1921, Congress approved the burial of an unidentified American soldier from World War I in the plaza of the new Memorial Amphitheater.