Launch on Warning

Posting this because I am interested in this: "Strategies are available that can reduce the effectiveness of a launch-on-warning stance. For example, the first-strike nation can use a technique called X-ray pin-down to delay a retaliatory response. It involves a barrage of submarine-based missiles fired from close range in a "depressed trajectory" mode that reaches its targets in minutes. The warheads would be set to explode every minute or so at high altitudes, which would significantly disrupt the attacked nation's ability to launch its own ICBMs."

How does this work in detail?