Late last year, as Islamic State fighters battled to expand their stronghold on Libya’s coast, ­militants came within 45 miles ­of the country’s sole remaining ­chemical-weapons site, unnerving Libyan and American officials who feared that potentially deadly chemicals could fall into extremist hands.

In May, when the fighters struck a mile from the lightly guarded desert facility, killing two security officers at a checkpoint, they decided it was time to act. Continue Reading.