Since Osama bin Laden was killed earlier this month by U.S. Navy SEALs not far from Pakistan's capital, Islamabad, there has been a wave of retaliatory attacks on various installations in Pakistan. That has raised concerns about the safety of the country's nuclear weapons.
One of the most brazen of the recent attacks happened last weekend, when armed militants scaled the wall of the heavily guarded Mehran navy base near the southern city of Karachi. They fought off Pakistan's military, including commandos, for 17 hours.