The Navy plans to buy 12 ballistic-missile submarines to replace the 14 current Ohio-class, or Trident, boats that are nearing the end of their service lives.

Now the Defense Department has notified Congress that the Navy will design the next generation of ballistic-missile submarines with the flexibility to accommodate female crew members.

The Missile Alternative Range Target Instrument is similar in size and geometry to a ballistic missile, but with a section of sensors to record and measure the laser performance.