By DAVID WILLMAN
REPORTING FROM WASHINGTON | JULY 6, 2016, 3 A.M.
If North Korea ever unleashed nuclear-armed missiles against America, the defense of U.S. cities and towns would depend to no small degree on something called a divert thruster.
These small rocket motors would be counted on to keep U.S. anti-missile interceptors on target as they hurtled through space toward the incoming warheads.
If the thrusters malfunctioned – and they have a record of performance problems – an interceptor could veer off-course, allowing a warhead to slip through. The consequences could be catastrophic.