Considering the Spitfire's chronic lack of range, was the RAF doing unescorted bombing runs over Nazi Germany in 1940-42 or did they have another fighter that escorted their bombers?
Most bombing by both the RAF and USAAF was partially or fully unescorted.
Early in the war, virtually all long-distance bombing raids took place at night to avoid the possibility of interception. The Germans used searchlights and AA guns to try to combat this. Later in the war they developed night fighters.
The United States eventually perfected daytime, high-altitude bombing. This required aircraft with oxygen supplies and masks, as well as a very sophisticated bomb sight.
The diagram below shows the evolving range of possible escort during the war:
As you can surmise from the diagram, before 1943 any bombing beyond the area of the English channel or other allied bases was unescorted.
The RAF, as a general rule, conducted all of their bombing operations against Germany at night. Escorts were not really necessary under these conditions and probably would have been more of a liability than any protection. The USAAF believed that they could conduct precision daylight bombing and executed their operations against Germany during the day. The American leadership initially believed that the B-17 and B-24 bombers were so heavily defended that they would not need to be escorted. When this was proven to be incorrect, it lead to the rapid and joint British-American development of the P-51 Mustang (North American air frame with a Rolls Royce engine). The P-51 became the best all-around fighter of the war. It should be noted that the British bombing operations at night were highly successful, albeit inducing civilian carnage that today's society would have fits over.