Lockheed Martin [LMT] on Monday said that Marillyn Hewson on June 15 will retire as president and CEO of the nation’s largest defense contractor and be succeeded by James Taiclet, the current executive chairman, president and CEO of American Tower Corp.

[AMT], a global provider of telecommunications real estate for wireless infrastructure.

Hewson, 66, who has served as chairman, president and CEO since 2014 and as president and CEO since 2014, will continue as executive chairman of the $59.8 billion defense giant subject to her re-election to the board at Lockheed Martin’s upcoming annual meeting.

The decision to retire from leading the company on a day to day basis was hers and Taiclet is her choice to lead Lockheed Martin going forward.

“I know it is the right time to transition the leadership of Lockheed Martin,” she said in a statement released by the company. “The corporation is strong, as evidenced by our outstanding financial results last year and a record backlog of business. We have a bright future—particularly with Jim and our outstanding leadership team at the helm. I’m pleased the board agreed with my recommendation. As Lockheed Martin’s next CEO, Jim will lead the company forward in its next phase of growth and value creation.”

In a separate post on LinkedIn, Hewson said, “Lockheed Martin is not just any corporation; it’s a national asset. We play an important role supporting our military forces keeping Americans – and allies around the world – safe and free. And we advance discovery and knowledge for the world. Love of company and love of country have always been intertwined during my career. So, it’s important as I leave the CEO role that this national asset is in top shape – financially strong, with a record $144 billion in orders, and a vibrant workforce.”

Taiclet, 59, has led American Tower since 2003, first as CEO and then a year later as chairman, president and CEO. Lockheed Martin said that Taiclet expanded American Tower from its U.S. roots and $2 billion market capitalization to a global business operating in 19 countries and a market capitalization of around $100 billion currently. The company has $7.6 billion in annual sales.

A member of Lockheed Martin’s board since 2018 who also sits on the company’s classified committees, Taiclet has impressed Hewson and other board members with his business smarts and knowledge of the company and defense industry. Before joining American Tower, Taiclet served as president of Honeywell Aerospace Services, a business unit of Honeywell International [HON], and before that was vice president of Engine Services at Pratt & Whitney, an operating segment of United Technologies Corp. [UTX].

Taiclet is a graduate of the U.S. Air Force Academy with degrees in engineering and international relations and began his career as an Air Force officer and pilot, serving a tour of duty in the Persian Gulf War. He also has a master’s degree in public affairs from Princeton.

Taiclet was also a consultant at the global management consulting firm McKinsey & Company where he specialized in telecommunications and aerospace strategy and operations.

American Tower leases space on communications towers and other assets to wireless telecommunications providers.

On a more personal level, Hewson said the timing of her semi-retirement will give her a well-earned break from nearly a lifetime of hard work.

“The timing is right not only for our company, but for me personally,” she said on LinkedIn. “I have worked full time since I was 16. So, when the transition is complete, I am looking forward to this new chapter of life with my husband James and our sons, who have been such supportive partners on my career journey.”

Lockheed Martin also said that Frank St. John, 53, who runs the Rotary and Mission Systems (RMS) segment, has been elected by the board to become chief operating officer (COO), a senior leadership position last held by Hewson prior to her becoming CEO. St. John will be succeeded by Stephanie Hill, 55, who is currently senior vice president of Enterprise Business Transformation. Their appointments are effective June 15.

St. John will report to Taiclet and be responsible for the company’s strategic, operational and financial performance across all lines of business. The heads of all four of the company’s operating segments–Aeronautics, RMS, Space, and Missiles and Fire Control (MFC)–will report to St. John.

St. John has been with the company for more than 30 years and Hill 23 years. Before leading RMS, St. John was executive vice president of MFC.

Hill is a former deputy executive vice president of RMS and senior vice president for corporate strategy and development. As head of Enterprise Business Transformation, she leads the Digital Transformation and Enterprise Information Technology teams.

“Marillyn and the board have been focused on developing talent and ensuring a high-quality succession plan,” Dan Akerson, Lockheed Martin’s lead director, said in a statement. He thanked Hewson for “demonstrating a strong commitment to the customer, shaping the company’s portfolio to meet the challenges of today’s global security environment and growing the business and driving long-term sustainable growth.”

With Hewson at the helm, Lockheed Martin sold its former $5 billion Information Systems and Global Solutions segment to Leidos [LDOS] and acquired the Sikorsky Aircraft helicopter company from UTC.