well longest range land based SAM sure, but since China seems have taken part in development process, i question the effectiveness of the system. The fact is the Chinese even copied its, though they don't have a missile that can hit 400km away. The fact is that the S-400 can handle targets with max. range of 3500km and max speed of 4.5km/second or a little over mach 13.2.
Now our PAD/AAD together have the ability to take care of threats with a max. range of 3500km. These PAD/AAD have gimballed warheads, can take care of Agni-2 style targets with speeds over mach 15. Hence our AAD/PAD have better ABM abilities than S-400.
Now LR/MR-SAM will be enough take take care of border air defense combined with AAD/PAD, Akash, Spyder SAMs. SM-3 interceptors have higher flight ceilings and longer ranges and can handle threats traveling well over 20,000km, based on ships they will give us good protection from naval attack. I would love to see upgraded SM-3/6 in our inventory. S-400 is a joke compared to that. Besides Raytheon is working on land based SM-3 interceptors.
SM-6 is ideal for Ship based air defense against maneuverable aircraft and cruise missiles, it has max range well over 180km.
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On February 21, 2008 at 3:26 am (UTC) the USS Lake Erie, a Ticonderoga-class guided-missile cruiser, fired a single SM-3 missile, hit and successfully destroyed the satellite, with a closing velocity of about 22,783 mph (36,667 km/h) while the satellite was 247 kilometers (133 nautical miles) above the Pacific Ocean.
Two new anti ballistic missiles that can intercept IRBM/ICBMs are being developed. These high speed missiles (AD-1 and AD-2) are being developed to intercept ballistic missiles with the range of 5000 km. The test trials of these two systems is expected to take place in 2011. The new missile will be similar the THAAD missile deployed by the U.S.A. These missiles will have to travel at hypersonic speeds and will require radars with scan capability of over 1500 kilometers to successfully intercept the target.
Since we are working on missiles to deal with ICBMs and by 2011 we'll test them and we'll have something much better than the S-400 or any Russian counterpart, forget the s-400, its no use for us.