Intruder Havoc Mk I BD121 YP-F in flight, Summer 1941
The intruder version of the Boston was designed for offensive patrols over enemy territory at night, targeting enemy aircraft and support infrastructure. Unlike the night fighter variant, the intruders maintained the standard bomb load of the bomber versions. The primary modifications for intruder missions included a different camouflage scheme, which evolved over time, and exhaust dampeners. Initial targets were Luftwaffe airfields in Belgium, the Netherlands, and northwest France.
The fixed nose armament, consisting of four 0.303-inch machine guns, was effective for attacking German aircraft at close range, especially during their approach and landing phases at airfields. Later in the war, as intruder operations expanded to include railway targets, the four nose guns proved insufficient for causing significant damage. Consequently, the forward-firing armament was augmented with a gun pack under the fuselage, consisting of four 20mm cannons. Additionally, the bombs were replaced with an extra fuel tank, providing a safe endurance of approximately four and a half hours.
When the Boston was phased out of intruder operations, many surviving aircraft reverted to their original bomber configuration and continued to serve operationally in units in Europe and North Africa. Some were also modified for other roles, such as the Turbinlite trials, or served as trainers. These modifications were relatively simple and inexpensive, unlike the more complex changes required for night fighter variants.