Apollo 8 did not carry a Lunar Module on this flight. The LM was not yet ready to be flown. The flight was simply for the CSM alone to go to the Moon, orbit, and return to Earth. This was accomplished Dec. 21-27, 1968. The Flight was well known for, among other things, the Christmas Eve broadcast where the crew (Lovell, Anders, and Borman) read from The Book of Genesis.
(NOTE- If there had been a problem like that which occurred on the flight of Apollo 13 in 1970 the crew would have perished)