Yes and No
Just went to Germany this summer. You don't need a visa. German consulate will give you a letter stating that. Make sure they do - sometimes they get confused on RTD vs. Advance Parole.
Secondly, I do think you need a transit visa for the UK. They have a good web site -look it up and make sure you get it all right.
Finally, before the day of your flight, make sure they clear you at the airline. Or get there early. Idiots at Delta would not let me on the flight b/cause they had not seen a RTD before. Ditto for letter from German consulate.
Good luck - have a great time!