Larry J said:

"As for decoys, they cease to be a problem if you can wait until the RVs begin entering the atmosphere. Lightweight decoys will decelerate very rapidly when entering the atmosphere compared to actual warheads, so discrimination is much easier. If the decoys are as heavy as the warheads, then you might as well make them warheads and have a MIRV capability."

Non-maneuvering RVs fly at zero angle-of-attack (ballistic entry). Their trajectory is driven by atmospheric drag so the vehicle's basic flight parameter is "ballistic coefficient" (beta) which is defined as:

beta = [vehicle mass, m] / ([Drag Coefficient, Cd] [base area, A])

The requirement for an effective decoy is the decoy's beta must be the same as the RV's, e.g. if mass is halved then Cd A must be halved as well. For a modern RV, the mass (density) is so large and the base area so small that it is difficult to make a decoy. Therefore with modern ballistic missiles, MIRVs are used instead of decoys. However with old fashioned RVs like the Mk-6 on the Titan-II, the RV was so big that decoys were practical (they did have issues getting the radar cross section right). An "Islamic" ballistic missile would probably use 1950s technology with a big RV carrying a single warhead. Also because the bad guy's nuclear isotope enrichment technology is primitive, they won't have much U-235 and plutonium to waste on MIRVs. Therefore, they'll probably use decoys.

Gary