The airplane had existed for little more than a decade by the outbreak of World War I, but both sides of the conflict quickly recognized the advantages of creating flying war machines and worked relentlessly throughout the war to develop faster, bigger and deadlier fighters and bombers. The concept of “air superiority” was unheard of before 1914, but winning the war in the skies became a tactical necessity by the end of the Great War.

The main military role of aircraft in World War I was reconnaissance, says Jon Guttman, a historian of military aviation who’s authored more than a dozen books about World War I aircraft and fighter pilots. Hot air balloons had been deployed by the military for more than a century to get a bird’s-eye view of the battlefield, including during the U.S. Civil War, but the fixed-wing airplanes of World War I were able to fly deep behind enemy lines to track troops movements and map terrain.

“These were two-seater aircraft with a pilot to do the flying and an observer up front to man the binoculars and take notes,” says Guttman.

The handwritten drawings and on-the-fly observations weren’t always accurate but proved critical in some early operations. In 1914, for example, British reconnaissance planes with the Royal Flying Corps alerted British and French commanders to German troops preparing for a siege of Paris through Belgium. The Allied armies were able to outflank the Germans, resulting in the Battle of the Marnes, a critical early victory.

It wasn’t long before cameras were mounted to reconnaissance planes, taking dozens of aerial photos that would be developed and stitched together to create panoramic battlefield maps. Those increasingly sharp and zoom-in images gave field commanders unprecedented intelligence for positioning artillery and planning troop movements.

At the start of World War I, reconnaissance planes were such a novelty that enemy pilots would wave at each other as they crisscrossed the front lines. But it wasn’t long before the strategic importance of spy planes sunk in, and with it a burning desire to shoot the enemy’s aircraft out of the sky.

“There was no such thing as a fighter plane until 1915,” says Guttman. “But after the Marne, military commanders began to take seriously the idea of eliminating the other guy.”

In early skirmishes, slow-moving reconnaissance planes would take pot shots at each other with service pistols and rifles. Ground crews started mounting machine guns in front of the observer’s position, but they were hard to aim around the propeller, wings and struts.

The breakthrough invention was the “interrupter gear” or “synchronization gear,” which allowed a front-mounted machine gun to fire a continuous barrage of bullets safely through the plane’s rotating propeller blades. All pilots had to do was aim the nose of the plane at the enemy and fire.

Dutch-born engineer Anthony Fokker is credited with developing the first synchronized gear for the German army which he mounted on the single-seat Fokker E-1 in 1915. The lightweight plane was so nimble and deadly that the Allies nicknamed it the “Fokker Scourge.”

For the first time, planes took to the air with the express purpose of air-to-air combat, and the French began calling any pilot who shot down five or more enemy planes a “l’as” or an Ace. While these Aces had no shortage of skill and daring, the winners of most early “dogfights” were the pilots flying the better technology.

“From the moment that fighters became practical, that was the real start of an arms race for air superiority,” says Guttman. “The performance of an airplane, its ease of handling, its armament, its rate of climb—all of these became factors in a constant struggle to come up with something better than what the enemy had.”

Allied engineers responded with their own single-seat fighters like the British-made Sopwith Camel, named for the hump-shaped bulge in its fuselage to fit two front-mounted synchronized machine guns.

When Sopwith introduced a three-winged “triplane,” the Germans answered with the Fokker DR-1, the favorite of none other than Manfred von Richthofen, the dreaded “Red Baron,” who was credited with 80 official kills before his red, the three-winged fighter was finally shot down in 1918.

We usually associate aerial bombings with Nazi Germany’s Blitzkrieg tactics of World War II, but the first targeted bombing campaign occurred in 1915 when Germany sent high-altitude Zeppelin airships on nighttime bombing raids of civilian targets in London and Edinburgh.

The hydrogen-filled Zeppelins, initially used for reconnaissance, cruised at 11,000 feet and could cut their engines to carry out surprise attacks. The British public decried the “baby killers” and the military finally deployed fighter planes armed with incendiary bullets to torch the massive Zeppelins.

The first bomber planes began their careers as reconnaissance aircraft that were loaded with more and more weaponry as they had to fight their way back from behind enemy lines. Guttman says that the biggest reconnaissance planes, like the four-engine Russian giant known as the Ilya Muramets, started carrying bombs to drop on the enemy “as a final insult.”

The Germans took a page from the Russian handbook and built their own massive bomber called the Zeppelin Staaken R.VI, a biplane with a wingspan of more than 138 feet that carried up to nine crewmembers. The feared German bomber made runs to London and Paris, dropping bombs weighing more than 2,200 pounds, including a direct hit on London’s Royal Hospital Chelsea.

By the end of World War I, it was “indisputable,” says Guttman, that airplanes were the weapon of the future. By 1918, Allied bombers were already flying in group formations to attack German munitions factories along the French border, and German fighters were deployed in force to wage epic air battles.

The stage was set for World War II, when air superiority was one of the deciding factors for the Allies in both the European and Pacific theaters.