The Bréguet Bre.4, also known variously as the Type IV and BUM, was a French biplane bomber of World War I.
A fighter version of it was also produced as the BUC and BLC; some of these saw service with the British Royal Navy, which called them ‘the Bréguet ‘de Chasse.
The Bre.4 was developed during 1914 when French military planners began to express a preference for pusher- over tractor-configured aircraft, leading Bréguet Aviation to cease further development of its original Type IV design and pursue military contracts with an aircraft of the preferred layout.
The Type IV was a two-bay, equal-span, unstaggered biplane that seated the pilot and observer in tandem open cockpits in a nacelle that also carried the pusher engine at its rear, and the tricycle undercarriage.
As the prototype neared completion, the Bréguet factory at La Brayelle, Douai was threatened by the advancing German Army, and the machine and its builders were evacuated to Villacoublay where construction and testing were completed.
At this point, André and Édouard Michelin approached the French government with an offer to sponsor the construction of 100 bombers for the French Army and were awarded a licence for the Bréguet design.
This was put into production as the BUM (B for pusher-driven, U for Canton-Unné-powered, M for Michelin).
A later revised version, the BLM, was the definitive Renault-powered version.
Soon after the BUM entered service, the French Army requested that an escort fighter version be developed to protect the bombers from interception.
Bréguet responded with a lightened design armed with a 37 mm (1.46 in) Hotchkiss cannon, intended to pick off enemy fighters before they closed to within range of their machine guns.
This entered production as the BUC (C for chasse, or pursuit) in its original Canton-Unné powered version and BLC in its Renault version.