"I was very young, and it was really my first time away home," says Hrivnak, 38, of Bethel Park, who has served in both Gulf wars and began keeping a diary during his first mission in 1990.
"There was a lot of anxiety about the upcoming war that night on Christmas Eve," he says. "At our field hospital, some British mercenaries had sponsored this Christmas Eve for us. ... I still get choked up thinking about this: Some big, burly, gruff guy with a great baritone voice got up and sang ‘Silent Night,’ the ‘Star-Spangled Banner’ and Great Britain’s national anthem.
"I can still see everyone’s faces. There was not a dry eye in the room."
That year, he wrote to his mother to tell her that although he wanted to be home for Christmas, spending it at the field hospital was one of the best Christmases he ever had.
Since the beginning of the U.S. military, with the 1775 formation of the Continental Army by 13 colonies seeking independence from Great Britain, troops have kept diaries and sent letters home -- and their thoughts and emotions, especially at Christmas, are a constant spanning that time.
"The formality of the language is the only thing that has changed over the centuries or over the generations," said Washington, D.C.-based author Andrew Carroll, founder and director of the Legacy Project, an organization that preserves personal wartime correspondence.
"The emotions from war to war are exactly the same," said Carroll, who estimates he has read more than 80,000 letters spanning the French and Indian War to the Iraq war.
It makes no difference whether a soldier is hundreds of miles from home, as many were during the Civil War, or 10,000 miles away, in the Middle East, Carroll said. It's still far from home.
"They are missing the traditions and rituals of their family, so they write home about these fond memories as something to cling to -- it is what keeps them going."
Hrivnak's sentimentalism and yearning for home at Christmas is not much different from that of Civil War Capt. John W. Patterson, who noted on Dec. 29, 1861, in a letter to his wife, Armira, on display at Soldiers and Sailors Memorial Hall in Oakland: "I ... had pleasant thoughts of Home(cq) and the loved ones there."
Patterson, of Birmingham, which became Pittsburgh's South Side neighborhood, was with the 102nd Pennsylvania Volunteer Infantry, Company E, at Camp Tennallytown when he wrote to her: "I trust that you will not fret about me. I am well and enjoy military life hugely and besides that I expect to live through this war and get home to my family and there remain. Do not therefore my dear Armira grieve at my absence."
Telling her that he believed he was doing a duty owed to God, his country and fellow man, his letter concluded: "If I only knew that you were happy during my absence, I would be much more happy myself. Therefore take the matter Philosophically(cq) and be a good girl. Trust in God and all will be well."
Patterson, who rose to the rank of colonel on Christmas 1863, did not live through the war, records show. He died at the Battle of the Wilderness in May 1864. His uniform and sword are in the museum's collection.
Civil War Sgt. J. Milton Ray wrote to his sister on Dec. 24, 1862, from camp near Fredericksburg, Va., with the 140th Pennsylvania Volunteer Infantry Company C: "We spent a very quiet Christmas. Tom Noble gave me a piece of fresh beef and we had beef and soup for dinner, which we relished very much."
In World War I, Cpl. Fred Wertenbach wrote in his diary on Dec. 24, 1918, while stationed in France with Company G, 111th Infantry, 28th Division of American Expeditionary Forces: "Xmas(cq) here was not so awfully bad. We had dinner of corn -- wooly, but given tobacco and chocolate."
The following day, Wertenbach, of Fineview, noted: "(With) Christmas there comes a sadness tonight. So many dead -- for what? How am I ever going to pick up the old existence again. A clerk! And dead men's faces leering at me from the row of figures. Peace on earth -- shall I ever find it again? ... It is 3,000 miles to the U.S., but untold millions to yesterday and the old scheme of things."
From war to war, over the years, the emotion that the season evokes is reflected in troops' letters, Carroll said.
"Whether you are going off to war with a musket or an M-16, it does not really matter in the letters and thoughts that are sent home," he said. "The technology and language may differ, but the message is the same -- it is the generosity of hope and longing for home that shines though each generation."
Hrivnak, who was a flight nurse with the Air Force Reserve, began writing home by scribbling on pieces of tape that he would stick to his leg as he flew with wounded soldiers to Germany for medical treatment.
"I would take those pieces of tape off late at night and use them as notes to jog my memory about what had happened that day," said Hrivnak, who retired in July.
He and his wife of eight years, Jennifer, 34, a major in the Air Force Reserve and also a flight nurse, met in Officer Training School near Montgomery, Ala. She has been deployed three times, and in August her unit is scheduled to return to Iraq, Hrivnak said. The couple have a 6-month-old son, John Dawson.
In her last deployment, Jennifer Hrivnak wrote from Germany to her husband just before Christmas 2005, describing how deeply she was affected by managing flights for the wounded and troops who were killed:
"We are not on the forefronts of the battle, or in harm's way, but we all have come to the realization that there is a war going on down there and has been going on for four years now.
"... Though we are not in the desert, fighting in the sand and heat, all of us here ... are affected by this war. We are away from our families for months and years. It is time lost that we will never get back.
"Most of all, we are deeply moved and forever changed by our most solemn duty, arranging and executing the final journey of our valiant precious cargo... Our heroes are returning home."