Reagan, who died on Saturday at the age of 93, launched the idea of an anti-missile shield with a simple appeal in a speech on March 23, 1983.

"I call upon the scientific community in this country, who gave us nuclear weapons, to turn their great talents to the cause of mankind and world peace; to give us the means of rendering these weapons impotent and obsolete," he said.

Only a handful of aides knew what Reagan planned to propose -- and most opposed it. Public reaction was positive but the experts were appalled and the press dismissed it as a science fiction pipe dream.

But more than two decades later Reagan's grand vision of defending the United States against nuclear missiles is still alive.

Amid the threat of nuclear attack by so-called "rogue states," President George W. Bush advocates unrestrained development of missile defenses, although debate continues to rage over its feasibility.

But Reagan's notion of an active defense against ballistic missiles has gained growing political acceptance in the United States, even as the technical limitations have become more apparent.

Reagan's appeal to the scientific community -- and billions of dollars in research money -- summoned into being grand plans for a layered defense against missiles, much of it from the "high ground" of space.

The Pentagon funded research into lasers, particle beams, precision sensors, "smart rocks."

Kinetic and directed energy weapons would in theory be used to knock down missiles in their "boost phase" and in mid-trajectory, while ground-based interceptors would take out missiles that "leaked" through the shield.

Later, the Pentagon explored a plan called "Brilliant Pebbles" that involved using swarms of "smart rocks" in space that would seek and destroy enemy missiles.

But in 1991, long before the new technologies were proven, the rationale for the "Star Wars" program collapsed with Soviet Union.

Washington found it could eliminate more Russian nuclear warheads through arms treaties than with "brilliant pebbles" provided it preserved the 1972 Anti-Ballistic Missile (ABM) Treaty, which bars space-based anti-missile systems.

But the 1991 Gulf War and development of a nuclear arsenal by North Korea provided a new rationale for a more limited missile defense system: the threat of rogue states.

The main US defense now in development has the more modest goal of intercepting several dozen missiles -- insurance against attack by a North Korea or an Iran -- but no match for Russia.

WAR.WIRE