Rapid advances in technology which had taken place in the late 1930s had rendered the Blenheim mostly obsolete by the outbreak of the war. In particular, it had become heavier as extra service equipment was installed; much of this was found to be necessary through operational experience. This, coupled with the rapid performance increases of the fighters that would oppose it, had eclipsed the Blenheim's speed advantage. In January 1941, the Air Staff classified the Blenheim as inadequate in terms of performance and armament for current operations.