General Dynamics [GD] yesterday said that its chairman and CEO Jay Johnson, 66, will retire at the end of 2012 and be succeeded by Phebe Novakovic, 54, who became president and chief operating officer of the defense company last month after leading the company’s Marine Systems division.

Novakovic’s ascension to the top spot at GD is no surprise but Johnson had not indicated previously when he planned to step down. Novakovic would be the first female chief of one of the nation’s top five defense contractors, which include Boeing [BA], Lockheed Martin [LMT], Northrop Grumman [NOC] and Raytheon [RTN], although some of these firms have women in key roles responsible for multi-billion dollar operations.

“Jay has provided strong leadership, guidance and service to our board, the corporation, its shareholders and the country,” Jay Crown, GD’s lead director on its board. “We are most grateful to him. Phebe is a strong leader who has great depth of knowledge about General Dynamics’ products, services, processes and customers.”

Johnson became CEO of GD in 2009.