In the battle at Shaduzup, the huge triangular sets of concrete blocks in the rail yard, where the close-in fighting took place, were originally built to support huge fuel tanks used to fill up the engines as they were leaving the yard.

Vaughan Wilson, who plays Gen. Merrill's aide-de-camp Bannister, was actually one of the members of Merrill's Marauders (as Lt. Col. Samuel Wilson), and served as Merrill's deputy during the campaign.

This historical epic film stars Jeff Chandler (in his final role) as Frank Merrill and several actors from the Warner Bros. Television stock company, who were then the lead actors in American television shows. The supporting cast features Ty Hardin from Bronco (1958), Peter Brown from Lawman (1958), Andrew Duggan from Bourbon Street Beat (1959), and Will Hutchins from Sugarfoot (1957).

While working on Merrill's Marauders in the Philippines, on April 15, 1961, Chandler injured his back playing baseball with U.S. Army Special Forces soldiers who served as extras in the film. He had injections to deaden the pain and enable him to finish the production. On May 13, 1961, he entered a hospital in Culver City, California and had surgery for a spinal disc herniation. There were severe complications; an artery was damaged, and Chandler hemorrhaged. On May 17, in a seven-and-a-half-hour emergency operation over-and-above the original surgery, he was given 55 pints of blood. A third operation followed, on May 27, where he received an additional 20 pints of blood. He died on June 17, 1961. The cause was a blood infection complicated by pneumonia. He was 42 years old.

The character Bannister was played by Lt. Col. Samuel Vaughan Wilson, who was an actual member of Merrill's Marauders and one of the few survivors of the actual campaign.

Continuity

When Stock and the rest of his platoon reach the top of the mountain, the lower part of the left sleeve on his shirt has been cut away. It remains like this for the rest of the film and isn't explained until the last battle. Stock has a wound on his arm and a bandage has been applied, but no wound was visible until after the final battle.

When Merrill and Stockton converse after the first battle, Merrill's pipe moves instantaneously to and from his mouth between shots.

When the troops are resting in the swamps, mud patches on Bullseye's arms appear and disappear between shots.

When Merrill is writing his letter at the railhead, the close-up shows his writing is well up in the top third of the paper, but in the wider shot he is seen writing under the middle of the page.



Factual errors

The role played by the Chinese Nationalist Army in the campaign is completely absent. In reality, troops from the 42nd and 150th Chinese Infantry Regiments of the X Force were a major part of the fighting; indeed the final victory at Myitkyina was only possible after Chinese reinforcements were flown in. The role of Japanese-American translators who served with the 5307th is also ignored.

The British officer incorrectly had his slouch hat pinned up on the right side. Commonwealth troops have always worn the slouch hat pinned up on the left side to accommodate left shoulder (sloped) arms.



Miscellaneous

Many of the men can be seen wearing their watches with the face on top of the wrist. They would actually have been on the underside to prevent reflection of the sun giving them away.

When Claude Akins is interacting with the soldiers who are eating their chow, he constantly has his finger on the trigger of his Thompson sub-machine gun, a safety violation in the field.

When the attack on the rail yard starts, a GI is shot as he crosses the rails. He falls down, and then, after he is down, he raises his arm up and drapes it across the rail.



Anachronisms

General Stilwell tells Merrill that he is concerned about the Japanese linking up with the Germans in India. This was a fear in 1942, when the Germans had conquered a vast expanse of Soviet territory, and it looked like they would reach the Caspian Sea and then Persia. But the German advance was turned back at Stalingrad in February 1943. At the time of the conversation in the movie, in early 1944, the Germans were being pushed out of Ukraine. They had no chance of linking up with the Japanese anymore.

When they reach the railroad and airdrops are scheduled, Will Hutchins' character watches the airplanes making the drops. The aircraft are Douglas C-124s which didn't enter service until 1950 - for the 1944 era of the movie; the aircraft would have been Douglas C-47 or Curtiss C-46 airplanes.