An unmanned U.S. Navy helicopter built by Northrop Grumman Corp and a precision ship-landing system built by Raytheon Co face mandatory reviews that could lead to their cancellation after quantity reductions drove unit costs sharply higher in 2013, the Pentagon announced on Thursday. Senior defense officials said the cost increases were largely due to cuts in the numbers of items to be purchased, but federal law required a careful look at program performance and other factors. The Nunn-McCurdy law requires a mandatory, 60-day live-or-die review if weapons systems see an increase of more than 25 percent in their unit costs.