Citing the growing Iranian missile threat, the United States announced plans last September to integrate sea- and land-based missile defenses in and around its NATO allies in Europe, referred to as the "phased adaptive approach".
"One of the elements of the intelligence that contributed to the decision on the phased adaptive array [approach] was the realisation that if Iran were actually to launch a missile attack on Europe, it wouldn't be just one or two missiles, or a handful," Gates said at a congressional hearing.
"It would more likely be a salvo kind of attack, where you would be dealing potentially with scores or even hundreds of missiles."
Gates voiced confidence that upgraded missile interceptors in development "would give us the ability to protect our troops, our bases, our facilities and our allies in Europe."
Gates said having those interceptor systems in place by around 2020 was critical not only because of the missile threat from Iran and North Korea, but also because "I think by 2020 we may well see it from other states, especially if we're unsuccessful in stopping Iran from building nuclear weapons".
Mixed messages
US officials and experts have at times sent mixed messages about the new system's capabilities.
At the hearing, Gates sought to allay concerns in Moscow about the new US approach by playing down its capabilities against the large-scale arsenal possessed by Russia.
"Our missile defences do not have the capability to defend against the Russian Federation's large, advanced arsenal. Consequently, US missile defences do not and will not affect Russia's strategic deterrent," Gates said.
"The Russians know that our missile defences are designed to intercept a limited number of ballistic missiles launched by a country such as Iran or North Korea," he said.
The Obama administration has held out the possibility that Moscow could take part in the missile defence system in partnership with the United States.
But Gates said: "There is no meeting of the minds on missile defence. The Russians hate it. They've hated it since the late 1960s. They will always hate it, mostly because we'll build it and they won't."
US intelligence agencies have long warned about Iran's growing missile threat and officials say anti-ballistic missile systems should cover all of Europe by 2018.
"We are clearly dealing with a country that has made no secret of its desire to develop a robust, plentiful, increasingly capable missile arsenal," Pentagon press secretary Geoff Morrell told a news conference.
But he said US intelligence on the Iranian missile programme was "an imperfect science".
"We have been proven wrong before. We have had to make adjustments," Morrell said.
He said the administration's approach to missile defence "will allow us the flexibility so that as intelligence changes, as the situation changes in these rogue states developing long-range and medium-range missile capabilities, we will have the wherewithal to adjust our defences."
The multibillion-dollar effort is designed to defend against Iranian missiles that could be tipped with chemical, biological or nuclear warheads, officials say.
According to US estimates, Iran could produce enough bomb-grade fuel for a nuclear weapon in as little as one year but would probably need three to five years to deploy a "usable" one.
(EurActiv with Reuters.)
