(Reuters) - Lockheed Martin Corp LMT.N said on Monday company veteran Marillyn Hewson will step down as chief executive officer, and tapped board member and American Tower Corp AMT.N boss James Taiclet as her replacement.

Hewson has been with the Pentagon’s largest defense contractor since 1983 and took over as chief executive in January 2013.

“The timing is right not only for our company, but for me personally.” Hewson said in a post on LinkedIn, adding she plans to spend more time with her family.

Under Hewson’s leadership, Lockheed stock has gained more than three-fold, thanks to expanded international demand, the F-35 fighter jet program and other military contracts that grew due to increased U.S. defense spending under President Donald Trump.

Michele Evans, who took over as executive vice president of Lockheed’s aeronautics division in October 2018, was widely seen as a leading candidate to succeed Hewson.

Frank St. John another Lockheed executive who began at the company as an intern had was also seen as a prospective successor. The company named St. John as chief operating officer when it announced Hewson’s successor.

Lockheed had changed its mandatory retirement age rules in 2018 to exempt the CEO, allowing Hewson to stay on past 2019.

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Taiclet has been the chairman, president and CEO of American Tower Corp, a REIT that invests and operates telecom assets, since 2004.

He has previously worked with Honeywell Aerospace Services, a unit of Honeywell International HON.N, and United Technologies Corp UTX.N in senior roles.

“Taiclet has an impressive pedigree based on his resume, but from an aerospace and defense perspective he is an unknown quantity,” said Robert Stallard an analyst at Vertical Research in a note on Monday morning. “But with Marilyn sticking around as Chairman, and a very experienced cohort of senior Lockheed managers, we are not expecting there to be any revolutionary change,” Stallard said.

Lockheed said the CEO changes are effective June 15.