Israel last week unveiled an improved precision, bunker-burrowing weapon, the latest in a series of operational upgrades aimed at honing what one official here labeled “a very credible military option” against the Iranian nuclear threat. Built by state-owned Israel Military Industries (IMI), the 500-pound MPR-500 is an electro-optical or laser-guided projectile that can penetrate double-reinforced concrete walls or floors without breaking apart. It is designed as an upgrade to the U.S. Mk82, thousands of which are in Israel Air Force stocks, and can use Joint Direct Attack Munition (JDAM) kits or Paveway for guidance.