America's missile defense program includes Fort Greely, Alaska, a far-flung military installation stocked with 26 missiles designed to blow up an enemy warhead, along with a similar complex at Vandenberg Air Force Base in California.

Citing the raising threats from North Korea, the Obama administration announced in March the U.S. will invest $1 billion in expanding Fort Greely's capabilities, adding 14 more intercepters by 2017. With four interceptors located in California, the expansion would increase the nation's ground-missile defense system by nearly 50 percent, bringing the total number of intercepters from 30 to 44.

But America's missile defense shield has long been controversial. Since 1985, the U.S. has spent nearly $158 billion on the program, with $8.3 billion allocated in 2012 alone. When adjusted for inflation, the total cost is roughly the same as sending a man to the moon during the 1960s Apollo Space program.

The U.S. has taken its ground-based defense system on 15 missile-killing test drives, racking up only a 53 percent success rate. Seven times since tests first began in 1999, bad sensors, guidance, rocket separation, software or launching errors caused the exercises to end in failure.

READ MORE: Can Fort Greely, Alaska shoot down a North Korean missile?