Wes Bush is stepping down as chief executive of Northrop Grumman Corp. at the end of the year and will be succeeded by Kathy Warden.
The move had been anticipated after Ms. Warden was elevated to chief operating officer last year, but the change comes at a crucial time for the big defense contractor making the B-21 long-range bomber and parts of the F-35 fighter jet produced by Lockheed Martin Corp.
Mr....