The ICBM is a missile launcher in Grand Theft Auto: London, 1969.
As implied the ICBM is meant to assume the appearance of a mobile intercontinental ballistic missile (ICBM) launcher, complete with an unspecified ICBM missile loaded on the vehicle. The launcher itself appears to be based on the body of the game's Fire Truck, with only the cab repainted green.
Being a large vehicle, the ICBM is heavier than even the Fire Truck but lighter than the Royal Pain, with a substantially low top speed, average acceleration, and poor brakes, grip and handling. Despite possessing a base export of value of £900, the ICBM cannot be exported as it is too large.
The ICBM is most prominently featured in a mission in GTA London 1969 where one ICBM is successfully stolen by Hans Nemesis until the protagonist, under Endeavour Chambers' orders, manages to find out the ICBM code and stops the ICBM from launching its payload.