In order to distinguish fighters from bombers, night fighters were given their own designation, Havoc. The first variant of the plane, equipped with an airborne radar, was named the Havoc Mk.I.
Another variant of the night ground-attack aircraft was given the name Havoc Mk.I Intruder (originally «Havoc Mk.IV»). Its main purpose was to attack German airfields on the coast of the English Channel at night, destroying enemy planes in the air and on the ground.
Alterations of the prototype bomber were few. The navigator's cockpit and the nose glazing remained intact. The gun and bomb armament was also left unchanged. Up to 1,100 kg of bombs could be suspended under the aircraft. Flame arresters were installed in the engine exhaust pipes.
Havoc Mk.I Intruders were used to block enemy airfields at night. The aircraft would fly over an airfield and concentrate its fire on planes that were taking off or landing, as well as on parking areas, hangars, and airfield equipment. From time to time, it would drop bombs, usually of a small-calibre, fragmentation type. Usually, a single Intruder would join formation with a group of enemy bombers returning from a combat mission, and they would lead it out to their airfield. After the landing lights were switched on, the Intruder's crew would attack the enemy air base.
Often, an Intruder would pretend to be a German aircraft that had dropped behind its group: it would fire signal flares over an enemy airfield and turn on its navigation lights as if about to land. If the ruse was successful, the night runway lights would be turned on on the ground, and sometimes the ground crew would even illuminate the runway with a searchlight. Then the Intruder would immediately attack the airfield which had revealed itself.
A bombing run while enemy aircraft were landing was particularly effective. In the process, they managed not only to destroy enemy planes on the ground but also cause panic among the anti-aircraft gunners, who would then open fire on all machines in the air, including their own. Sometimes, after several of these raids in a row, the Germans would even open fire on their own aircraft, assuming they were British «blockers».
A total of 27 French DB-7s were converted to Havoc Mk.I Intruders.