The SS18 mod 4 has the most kiloton payload 8000KT and the close comparable to US minute man II 4000KT.  The SS-27 does not orbit the earth as this would be a violation of Start II or some other treaty I think.  The SS-18 MOD 3 ( R-36O ) is a fractional orbital bombardment system were the entry vehicle enters a lower earth orbit and deorbits near its target and attacks.  Using fobs the R-36O has unlimited range and can kind of attack from any direction.  It is called FOBS because I think they do not ever let it make a full orbit around the earth because of some other treaty.  The R-36O was opeartional some time during vietnam and remained active until 1983.  I believe all other ICBM use a ballastic tragectory.  Meaning they go up and down in a predicatable way.  kinda of like the old computer game scorched earth or worms.  The ss-27 asides from being the fastest man made moving object inside the earths atmosphere also has a maneuverable warhead. Since SS-27 designed post smart-2 is a single warhead nuke.

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The soviets as always are the leaders in ICBM technology.

Bush and Putin changed all the nuke treaties up so I think now MIRV are no longer banned...