MOUNT GRETNA, Pa. -- During a steamy summer 100 years ago, Soldiers of the Pennsylvania Army National Guard trained at this site to protect the Mexican border. It would be the first time National Guard troops federalized as part of the Army.In June 1916, a crisis was brewing on the border. Mexican revolutionary commander Gen. Francisco "Pancho" Villa had crossed the border and raided several U.S. towns including Columbus, New Mexico and Boquilla, Texas.On June 18, 1916, the secretary of War on behalf of President Woodrow Wilson issued a call to the governors to mobilize the entire National Guard. Responding to Wilson's call-up, Pennsylvania Gov. Martin Brumbaugh authorized the Pennsylvania Guard to mobilize.Several units of the 7th Division (the predecessor of the current 28th Infantry Division) arrived at Mt. Gretna on June 23 to begin their encampment. The units mustered were the First Brigade, consisting of the 1st, 2d and 3d Infantry Regiments, The Second Brigade, with its 10th, 16th and 18th Regiments, the Third Brigade with its 4th, 6th and 8th Regiments as well as the 1st Cavalry, the 1st Artillery, Signal Troops, Field Hospitals and Ambulance Companies.The Soldiers received inoculations including smallpox and anti-typhoid. They also received physical exams to determine their fitness for duty. Men who passed the physical were mustered into federal service by July 4.Commanded by Maj. Gen. Charles M. Clement, the division arrived in El Paso and had set up camp by July 25. Life along the border proved to be good training for the troops. Unbeknownst to them at the time, they would be mobilized soon after for WWI. The troops participated in marches, artillery practice, and maneuvers along the border. Pay scales had improved for Guardsmen -- a 1st Sgt. could expect to make $11.25 a day, whereas sergeants and cooks made $7.50 and privates and musicians made $3.75.Additional units from the Pennsylvania National Guard continued to train at Mt. Greta and rotate to the border for the remainder of the fall of 1916 and the spring of 1917. By March all the troops had returned home.While today's National Guard seamlessly integrates with active duty counterparts, it was an untried concept in 1916. Prior to then, National Guard troops stayed as a unit when serving in a federal capacity such as the Civil War. This operation represented the first time that National Guard troops and their active-duty counterparts were comingled to form larger units.The Pennsylvania National Guard Military museum located on Fort Indiantown Gap displays several artifacts from this operation."The holdings of the Pennsylvania National Guard Military museum include not only hundreds of photographs of the various units of the National Guard of Pennsylvania at Camp Stewart at El Paso, Texas, but also weapons, field equipment, uniforms and a full-size horse fully equipped and his rider, a lieutenant in uniform circa 1916," said Charlie Oellig, the museum's curator.---The museum is open Mondays and Fridays from 10 a.m. to 4:30 p.m.Information for this article was gathered from "The First Century: A History of the 28th Infantry Division" by Robert Grant Crist and "History of the 10th Pennsylvania Volunteer Infantry Its Forebearers and Successors."