"In popular press legend it is often claimed that this bomber was attempting to attack Buckingham Palace but in fact it wasn't going to attack anywhere, because it had already been abandoned by its surviving crew, and was flying on autopilot by the time Ray Holmes rammed it.
The Dornier was from I/KG 76 and flown by Oberleutnant Robert Zehbe, and was part of a mission to bomb the railway lines running between Clapham Junction and Battersea power station. However the formation had come under heavy attack, and Zehbe's aircraft had been badly hit with two crewman dead, so Zehbe ordered the two other crew members to bale out, he then set the aircraft on to autopilot and baled out himself. The bomber flew on, as part of the formation at first, but soon the main formation changed course, and the abandoned bomber flew on alone, until its meeting with Ray Holmes."
source, The Most Dangerous Enemy, A History Of The Battle Of Britain. By Stephen Bungay

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For the first time I have seen "History" at close quarters,and I know that its actual process is very different from what is presented to Posterity. - WWI General Max Hoffman