On the first official Thanksgiving holiday in 1863 Union troops took a break from the fighting to enjoy an actual sit-down dinner.
Thanksgiving holiday  WWI

Head table with guests at the Thanksgiving dinner with the First Regiment, U.S. Naval Training Camp, Charleston, South Carolina, c. 1917
Admiral William Halsey having Thanksgiving dinner with the crew of battleship USS New Jersey, his flagship. 30 November 1944
US Army Troops Roadside for WWII Thanksgiving Dinner
WWII Troops line up outside Alexai Point Airbase mess hall for Thanksgiving
25 November 1943
WWII GIs enjoy Thanksgiving dinner-Poltava Airbase-Russia November, 1944
WWII Thanksgiving dinner, Italy, 1944
USMC Lieutenant Colonel W. W. Stickney preparing to cut a Thanksgiving holiday cake with a captured Japanese sword, Guadalcanal, Solomon Islands. 26 November 1942.
British and U.S. military members carve a turkey at the American Theatre Wing State Door Canteen in New York, Nov. 26, 1942.
Thanksgiving in Italy, 1944
Thanksgiving Day Service Held in English Country Church- Americans in Cransley, Northamptonshire, England, UK, 23 November 1944 Men of the US Army Air Corps listen to a sermon on ‘The Source of our Strength” during a Thanksgiving service at Cransley in Northamptonshire.
Thanksgiving in Korean War
North Korea, 5th Marine Regiment has Thanksgiving dinner of turkey, pumpkin pie, and trimmings. 22 November 1950
President Eisenhower Eats With Troops During Korean War
Thanksgiving Korean War
Thanksgiving Battle of Chosin Korean War
Soldiers line up for their Thanksgiving meal, 1966
Thanksgiving Vietnam
Thanksgiving Vietnam
Thanksgiving Vietnam
President George H.W. Bush shared Thanksgiving with the troops in Saudi Arabia in 1990 as they got ready to invade Iraq for Desert Storm a few months later.
In 2010 Gen. David Petraeus, CENTCOM commander, served turkey to sailors (including Petty Officer Third Class Albrian Crisotomo) while visiting the USS Nimitz (CVN 68) underway in the Persian Gulf.
Those who get to eat their turkey in the comfort of a dining facility are relatively lucky. Here soldiers are assigned to the 173rd Airborne Brigade sit down for dinner at Combat Outpost McClain in 2012.
Thanksgiving, Iraq
CENTCOM
Chief Aviation Ordnanceman Robert Flake, from Fort Smith, Ark., serves himself aboard the USS George H.W. Bush (CVN 77) during Thanksgiving 2013.
Sailors give thanks before enjoying their Thanksgiving meal aboard the aircraft carrier USS George Washington (CVN 73)
Thanksgiving Meal  USS Gerald R. Ford