When we are first introduced to the Batmobile in Batman Begins, we are told that the Vehicle was built initially as a 'bridging' vehicle to allow ground troops or heavier armour easier access into war-torn areas.
The bridging function didn't pan out, but the heavily armoured stealth vehicle turned out to be exactly what Batman needed.
However, there was no mention of the 'detachable motorbike' capability in the first film. Was this retroactively added to the vehicle? (Either in canon, or by the director) Or was the design for the 'Bat bike' included in the original design for the entire vehicle?