WASHINGTON (REUTERS).- An American soldier stands alone amid the long grass of a Vietnamese field accompanied by the helicopter that brought him there while a few other soldiers are seen in the background. “Landing Zone,” a somber depiction of the Vietnam War in 1966 by soldier John Wehrle, is among about 300 paintings by U.S. servicemen and women that will be unveiled to the public for the first time at Philadelphia’s National Constitution Center in September. The paintings have been selected from about 15,000 collected by the U.S. Army since the 1840s. Most have never been on public display. “Art of the American Soldier” focuses on the duties, sacrifices, and everyday lives of troops, and covers every conflict from the World War One to Afghanistan. The depiction of war through painting gives it an emotional dimension that photography cannot match, said Col. Peter Crean, deputy director of the Army Center of Military History. “War is a totally emotional experience, and the medi