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Breguet Bre.4 / BUC / BLC / BUM


Developed during 1914 when French military planners began to express a preference for pusher- over tractor-configured aircraft, leading Breguet to cease further development of its original Type IV design and pursue military contracts with an aircraft of the preferred layout.  The Bre.4 evolved indirectly from the BU3 two-seat twin-boom pusher biplane of late 1914 as a smaller and lighter development of its bomber derivative, the BUM (B=Breguet, U=Salmson engine and M=Michelin-built),  the BUC (the letter "C" signifying Chasse) was intended primarily as a bomber escort.

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 Breguet factory at 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 Army, and were awarded a licence to the Breguet design.

This was put into production as the BUM (B for pusher-driven, U for Canton-Unné-powered, M for Michelin), and later revised to the BLM as the definitive Renault-powered version.

With the installation of a 220hp Renault 12Fb 12-cylinder water-cooled engine in place of the Salmson, prototype trials were performed in June 1915, a few additional aircraft being built under the designation BLC.

Soon after the BUM had entered service, the French Army requested that an escort fighter version be developed to protect the bombers from interception. Breguet responded with a lightened design armed with a 37 mm (1.46 in) Hotchkiss cannon on a flexible mounting in the forward cockpit of the fuselage nacelle 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 200hp Salmson Canton-Unné  14-cylinder radial powered version and BLC in its Renault version. Few of these escort fighters were built, as their performance and utility were discovered to be lacking, and the doctrine of the cannon-armed escort fighter was soon abandoned in favour of countering fighters with other similar fighters. A number of BUCs were also built for Britain's RNAS using British engines.

The performance of both the BUC and BLC versions of the Breguet de Chasse was unspectacular and, with fewer than 20 delivered, they were declared obsolete by the Aviation Militaire before the end of 1916. During that year, a 17 essentially similar aircraft were supplied to the Royal Naval Air Service. These differed from the BUC/BLC primarily in having the 225hp Sunbeam Mohawk 12-cylinder engine, armament being a single 7.7mm Lewis machine gun (which was an alternative weapon to the Hotchkiss on French machines). The RNAS was disappointed with the performance of the Breguet de Chasse, which proved unsuitable for employment in the fighting role, and the service withdrew the type from its first-line inventory in June 1916.




Take-off weight: 1535 kg / 3384 lb
Empty weight: 1160 kg / 2557 lb
Wingspan: 16.40 m / 54 ft 10 in
Length: 9.50 m / 31 ft 2 in
Height: 3.70 m / 12 ft 2 in
Wing area: 54.0 sq.m / 581.25 sq ft
Max. speed: 138 km/h / 86 mph


Type IV (BU3)
Breguet prototype.
BUM (BrM2B.2)
Michelin-built, Canton-Unné-powered bomber version.
BLM (BrM4B.2)
Michelin-built, Renault-powered bomber version.
Michelin-built, Canton-Unné-powered escort fighter version.
Michelin-built, Renault-powered escort fighter version.
Breguet de Chasse
Version of BLC for RNAS, powered by Sunbeam Mohawk or Rolls-Royce Falcon engine.





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