Adding to the problems, as the warhead weight dropped, existing missiles had leftover throw weight that could be used for various radar decoys, which Zeus proved unable to distinguish from the actual RV.

It was intended primarily to protect against the very small Chinese ICBM fleet, limited Soviet attacks and various other limited-launch scenarios.

A full-scale attack by the Soviets would easily overwhelm it.

It was designed to allow gradual upgrades to provide similar lightweight coverage over the entire United States over time.

A new design emerged, Nike-X, with the ability to defend against attacks with hundreds of warheads and thousands of decoys, but the cost of the system was enormous.

Looking for alternatives, the Sentinel program offered a lightweight cover that would protect against limited attacks.

Sentinel began construction in 1968 but ran into a firestorm of protest over its bases being placed in suburban areas.

Nixon announced that Sentinel would be cancelled and redirected to protect the missile farms, and that its bases would be placed well away from any civilian areas.

In military circles, the most basic argument against Safeguard was that adding an ABM requires the Soviets to build another ICBM to counter it, but the same is true if the US builds another ICBM instead.

The Air Force was far more interested in building more of their own ICBMs than Army ABMs, and lobbied against the Army continually.

In the public sphere, opinion by the late 1960s was anti-military in general, and in an era of ongoing Strategic Arms Limitation Talks the entire concept was derided as sabre rattling.

Safeguard had been developed to calm opposition but found itself just as heavily opposed.

Nixon pressed ahead in spite of objections and complaints about limited performance, and the reasons for his strong support remains a subject of debate among historians and political commentators.

The Anti-Ballistic Missile Treaty of 1972 limited the US and Soviet Union to two ABM sites each.

Safeguard was scaled back to sites in North Dakota and Montana, abandoning initial work at a site in Missouri, and cancelling all other planned bases.

Construction on the two remaining bases continued until 1974, when an additional agreement limited both countries to a single ABM site.

Mickelsen Safeguard Complex, became active on 1 April 1975 and fully operational on 1 October 1975.

By that time the House Appropriations Committee had already voted to deactivate it.

The base was shut down on 10 February 1976.

This was essentially an upgraded version of their Nike B surface-to-air missile (SAM) along with dramatically improved radars and computers able to detect the incoming reentry vehicles (RVs) and develop tracking information while still leaving enough time for the interceptor missile to climb to its altitude.

Zeus had limited traffic handling capabilities, designed to deal with a small number of attacking missiles arriving over a period of as long as an hour.

However, in an era when ICBMs cost about the same as a strategic bomber, such an attack would cost an enormous amount.

This meant that much smaller rockets could carry these new warheads to the same range, greatly reducing the cost of the missile, making them far cheaper than bombers or any other delivery system.

When Nikita Khrushchev angrily boasted that the Soviet Union was producing new missiles like sausages, the US responded by building more ICBMs of their own, rather than attempting to defend against them with Zeus.

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