The Iraqi missiles which have twice come close to hitting US aircraft over Iraqi No Fly Zones are reported to be an advanced version of the Russian-built SA-6. These have several operating modes, including radar, optical, and heat-seeking. Reports indicate that the missiles were fired in ballistic mode and sent command guidance by ground units using optical tracking, which could explain why the two targeted aircraft had no warning they were under attack. In theory, this type of tracking could only be effective against a target that was flying "straight and level". The U-2 was flying at 70,000 feet when the missile exploded close enough for the pilot to feel the shockwave, apparently confirming reports that Iraq has extended the range of its SAMs with extra fuel tanks.--Stephen V Cole