The Iraq campaign reminded people that the M-1 tank has more types of ammunition than the discarding sabot and HEAT. There is now the MPAT (multipurpose anti-tank) and SMART (Smart Target-Activated Fire and Forget). Both of these are HEAT rounds with radar guidance systems. MPAT is like the usual HEAT round, but with more fragmentation effect, and less armor penetration. MPAT also has a radar fuze, which detects an aircraft in flight. When the radar system calculates that it is moving away from its target, after recognizing that it was moving towards it, the warhead detonates, showering the aircraft (usually a helicopter) with blast and fragments. This is often enough to bring down a helicopter, or at least damage it enough to put it out of action. The MPAT concept is an old one; the first shells with radar fuzes were produced during World War II. Developments in miniaturized radar led to development on the SMART round in the 1990s. This shell uses a radar and a smaller HEAT warhead that generates an armor piercing plasma jet that hits a target below the shell. The idea was to produce a shell that can attack vehicles hiding behind obstacles, or vehicles with frontal armor tough enough to resist discarding sabot rounds. While SMART worked in tests, there's not enough perceived need for it to justify putting it into production.