Messerschmitt Bf 110
'Heavy Fighter' might have sounded like a good idea at some point in the 30's, but ultimately proved a bad one by the time the Battle of Britain came round in 1940. After being mauled by Spitfires and Hurricanes the Messerschmitt 110 kept out of the way of single engined fighters and tried other jobs such as night fighting.
Kept in service even longer than it should have because of delays in getting a replacement (see Me210/410), the ageing 110 was loaded with mortars and sent in to break up the formations of USAAF bombers flying over Germany. As long as they were out of range of allied fighter escorts it did so with relative success.