In an era when wireless communication was still primitive, armies in World War I depended on a range of methods to relay messages between units. Options ranged from the telegraph to telephones to colored flares, mirrors that reflected flashes of sunlight, bugles and trained dogs and pigeons. But the most reliable means of communicating along the front was in the form of one of the war’s most dangerous roles: the runner.

Human runners were more dependable than staticky connections on phone lines. They could memorize complicated messages in case the papers they were carrying were destroyed or became illegible. And they could locate hard-to-find places.

Doran Cart, a senior curator at the National World War I Museum and Memorial in Kansas City, Missouri, explains that since keeping in contact with other flanking units was essential for survival, each army had its own runners who were ready to set off with critical updates.

Runners were usually low-ranking non-commissioned officers, such as corporals, who were chosen for their fitness, stamina and ability to read maps, Cart explains. They also had to be tough and resourceful enough to find their destination in any sort of weather, and sufficiently lithe and agile to navigate obstacles. As they ventured beyond their unit’s position, they faced the risk of being shot or blown up before they got there, or on the way back.

Of all the jobs in the infantry, “the runner’s job was the hardest and most dangerous,” World War I veteran Lt. Allan L. Dexter observed in a 1931 newspaper article. “With a runner, it was merely a question of how long he would last before being wounded or killed.”

“It was a thankless job,” Cart says.

For most of the war, runners usually stayed within the extensive, multi-layered trench network along the front lines. “You didn’t get out on the open ground, because of snipers and machine gunners,” he says. They traveled what might seem like short distances, usually yards rather than miles as the crow flies. “Most trenches were zig-zag patterns,” Cart explains. “You could run a mile in a zig-zag trench, but you’d actually go only three hundred feet.”

In the late stages of the war, when the Allied forces were on the move, runners played the crucial role of maintaining communications between units that might be advancing at different speeds, according to Paul Grasmehr, a reference coordinator for the Pritzker Military Museum & Library in Chicago.

But traveling even over short distances was a difficult challenge because it was hard not to get bogged down in the ever-present mud at the front. “By 1917, after years of artillery bombardment, you had craters filled with water, a horrible moonscape,” Grasmehr says.

To enable them to be more mobile and agile, runners were more lightly equipped than the typical soldier. Instead of a field pack and a rifle, “they generally had a sidearm, a haversack, and a canteen,” Cart explains. “If it was after 1916, they’d be wearing a steel helmet, and they’d always have a gas mask.”

Because even the short journeys were so risky, often multiple runners were sent out. As Sgt. Alexander McClintock, an American who served with Canadian forces in France, said in a 1918 newspaper account, “It is the rule to dispatch two or three or three runners by different routes so that one at least will be certain to arrive.”

Without such redundancy, disaster could result. McClintock described an assault on a German position in which an officer assumed that sending one runner with a message about a last-minute change of plans would do. But after that man was killed by a German bullet, his message went undelivered, and as a result, a battalion attacked the Germans without barrage fire to protect them. Some 600 men were killed or wounded in a few minutes. “Several officers were court-martialed as a result of this terrible blunder,” McClintock wrote.

Those who volunteered for the job of runner were regarded with great respect by others who served. As Elton Mackin wrote in his memoir Suddenly We Didn’t Want to Die: Memoirs of a World War I Marine, “A fellow didn’t have to take a runner’s job. All a fellow had to do was say no. Except in a pinch, when there was neither time nor choice, no one served as a runner except a volunteer, for many vital things depended upon the men carrying the messages.”