Multi-engined bombers saw use on the Western and Italian Fronts, although they generally were used for more strategic operations than the Ilya Muromets was.

Italy would have a large force of three-engined bombers made by Caproni that it would use for bombing of targets behind the frontlines. Along with Russia, Italy would be the only power to enter the war with a multi-engined fixed-wing heavy aircraft. Starting with the Ca.1 in 1915, the design went through several iterations featuring minor improvements and more powerful engines by the end of the war. Several hundred would be in service, equipping Italian and American Expeditionary Force squadrons on the Italian and Western Fronts respectively. The Italians would strike airfields and railyards, although they avoided cities. They did threaten to bomb Vienna in August 1918, dropping leaflets from a single-engined Ansaldo SVA warning of an impending bombing raid, but the bombing raid was never launched.

Britain had developed several heavy bombers that made it to service, most famously the Handley Page Type O. Type Os made several strategic raids on Ottoman naval forces in the Sea of Marmara (aimed at the Goeben) as well as strategic targets in cities, operating out of the island of Lemnos. The Type O's more famous use came in France, where it was deployed to hit strategic targets - particularly rail junctions - behind German lines. Britain would also have the twin-engined Vickers Vimy that would see service as a bomber after the war, but it was relegated to antisubmarine and maritime patrol duties during the war. The Handley Page V/1500 was a much larger design intended to be capable of striking Berlin, but it would only enter service in October 1918, and it would never get a chance to prove its worth.

All of the Allied efforts, however, were really overshadowed by the Germans. Zeppelins of the Imperial German Navy had conducted strikes on Liege in the opening days of the war. More famously, they began a strategic bombing campaign against Britain in 1915, although their efforts were largely ineffective. It wouldn't be until the introduction of the fixed-wing heavy bombers in 1917 that the raids on Britain were particularly damaging. Work had begun in 1915 on a series of aircraft that would be known as Grossflugzeug and the even larger Riesenflugzeug. G-series aircraft, most famously the Gotha bombers, were produced in the hundreds and could conduct raids of 20-30 aircraft at a time faster and more consistently than the Zeppelins ever could. Daylight raids in mid-1917 resulted in hundreds of deaths and injuries on the ground. The bombing campaign shifted to night raids by Fall 1917, with the first Riesenflugzeug joining the G-bombers in September. The G-bombers would be the backbone of the force through the end of the war - although the Riesenflugzeug had some record-setting characteristics, they wouldn't ever be available in large numbers, and typically fewer than five at a time were participating in raids. Many Riesenflugzeug were one-off designs with very unconventional layouts, and only the Zeppelin-Staaken R-series would see anything close to regular use. Overall, though, the strategic bombing campaign seems a bit unimpressive in retrospect - over the course of the war, fewer than 300 tons of bombs were dropped, and total casualties were under 1,500 dead and 3,500 injured.

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