JERUSALEM — After two decades of research and experimentation, Israeli defense officials now say they have a working prototype of a high-powered laser gun that can intercept rockets, mortar shells, drones and anti-tank missiles in flight. Officials said that the system performed successfully in a recent series of live fire tests in the southern Israeli desert, destroying a rocket, a mortar shell and a drone, and prompting a standing ovation from officials watching the action onscreen. The government has allocated hundreds of millions of dollars to develop the weapon, which Prime Minister Naftali Bennett described this week as a “strategic...