By the 1950's, the USSR started to develop their later-famous SCUD missiles, short-to-intermediate range nuclear-capable ballistic missiles. They were mounted on what essentially were heavy-duty trucks and were able to keep up with advancing armies. This abided with the USSR war doctrine, which entailed softening the enemy up with short-range nuclear strikes and following up with masses of Tanks and Mechanized Infantry. Yet the SCUD had an another advantage: while an aircraft could be detected by radar, and even a submarine could be hunted down by specialized forces, truck-based launchers were extremely difficult to find, as they were easy to both hide and re-locate. If operating in uninhabited areas, like deserts, forests or tundra, even the best spies would struggle to secure any information on them.