After World War I commenced in 1914, Sikorsky went on to construct roughly 80 more of the giant craft, which were pooled into an elite formation known as the Vozdushnykh Korablei (Flying Ships) Squadron. On February 15, 1915, they commenced a concerted, two-year bombardment campaign against targets along the eastern fringes of Germany and Austria.
In August 1914, the Ilya Muromets was adopted by the Imperial Russian Air Force. On 10 December 1914, the Russians formed their first 10-bomber squadron, slowly increasing the number to 20 by the summer of 1916. During World War I, the Germans often refused to attack Ilya Muromets in the air due to their defensive firepower. On 12 September 1916, the Russians lost their first Ilya Muromets in a fight with four German Albatroses, three of which it managed to shoot down. This was also the only loss to enemy action during the war, while three others were damaged in combat, but managed to return to base to be repaired.
The heavy bombers of other participants appeared in 1916, all resembling the Russian pioneer to a certain degree. The Russian government and Sikorsky himself sold the design and production license to the British and the French. The Germans tried to copy its design, using the fragments of the example they had shot down over their territory in September 1916.
By the end of 1916, the design was generally believed to have exhausted itself. The ensuing modifications, such as additional armor, made the aircraft too heavy and not worthy of upgrading. Even though the English, French and German bombers were faster, Sikorsky decided to switch to a new type of aircraft he would call the Alexander Nevsky.
The Russians built 73 Ilya Muromets bombers between 1913 and 1918. During this period, the Russians were the first in aviation history to perform bombing from heavy bombers, bomber group raids on enemy targets, night bombing and photographic bomb damage assessment. They were also the first to develop defensive tactics for a single bomber engaged in an air combat with a number of enemy fighters. Due to systematic weapon upgrades, the effectiveness of bomb-dropping reached 90%. The Ilya Muromets performed more than 400 sorties and dropped 65 tons of bombs during the war.
The last flight of an Ilya Muromets bomber took place in 1922 at the Air Shooting and Bomb-dropping School in Serpukhov.
The most common model of the Ilya Muromets was the S-23 V, with 32 built 1914-1916. The most common configuration, reportedly used for 22 of the 32 V aircraft.