The real General is seen boarding a US transport plane. The aircraft clearly has an incorrect paint scheme and, much more problematic, is a Fairchild C-82. A type that first flew months after D-Day while the film is set sometime before.
The opening title sequence is a car chase - Jeeps driving through wartime London. But many parked cars are clearly models from the 1950s. For example: Hillman Minx, Morris Minor, Ford Zephyr can all be seen.