Lockheed Martin chief executive Marillyn Hewson is moving on after seven years at the helm of the world’s largest defense contractor, stepping down from a role that made her one of the most influential members of the global defense industry.

James Taiclet, a longtime defense executive who currently serves as chief executive of American Tower Corp., will take her place effective June 15, the company announced Monday.

Hewson is leaving the company after several years of booming financial growth, with the expansion of the F-35 Joint Strike Fighter program taking the company to historic highs. In the latter half of her tenure, the company rode swelling defense budgets as the Pentagon under a Republican-controlled White House and Congress dramatically expanded purchases of fighter jets and other defense hardware.

At $40.5 billion, Lockheed is the largest recipient of U.S. federal contract dollars by a long shot. Its closest competitor, Boeing, received $19.7 billion.

In a letter posted on LinkedIn shortly after the news was announced, Hewson described Lockheed as “a national asset” whose role in supporting military forces sets it apart.

“Love of company and love of country have always been intertwined during my career,” Hewson wrote. “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.”

Hewson’s tenure began abruptly, when Lockheed in 2012 fired Chris Kubasik, its incoming chief executive, after he admitted having an improper relationship with a subordinate.

The sudden move thrust Hewson, a careful and soft-spoken executive from Kansas who started her 35-year career at the company as an industrial engineer, into one of the most high-profile positions in the business world. She soon grew into the role, meeting regularly with presidents and heads of state worldwide, boosting international sales, and guiding the company through an immensely profitable period. She also oversaw the $9 billion acquisition of Sikorsky, a major helicopter manufacturer.

“Marillyn has accomplished more than anybody thought was possible when she first became CEO,” said Loren Thompson, a defense consultant who has worked with Lockheed. “This is probably the best any defense company has done in the history of the industry. She had set the pace for the sector.”

But during her tenure, the F-35 program, the most expensive procurement in the history of the Pentagon, suffered problems before eventually stabilizing as prices fell and the company regained the trust of defense officials. In recent months there have been reports of continued problems.

While the company could rely on its F-35 for steady revenue from the Pentagon, Hewson sought to broaden the company’s portfolio by boosting international sales and investing in new technologies as autonomy and artificial intelligence were disrupting the weapons industry.

As Lockheed’s first female CEO, she was routinely named one of the most influential women in business and helped touch off a wave of defense companies hiring women in top leadership positions in an industry long dominated by men.

“Over time, the people who objected to her promotion were gradually eased out of the company,” Thompson said. “Marillyn ran a tight ship, and people who couldn’t live with having a woman at the top basically had to look for employment elsewhere.”

Hewson’s successor, Taiclet, serves as chief executive of American Tower, a publicly traded telecommunications real estate company. Taiclet previously held executive positions at Honeywell Aerospace Services and at Pratt & Whitney, both of which supply advanced fighter-jet components. He was appointed to Lockheed Martin’s board in 2018.

Before entering the business world, Taiclet was an Air Force pilot flying fighter jets and transport aircraft. He flew one of the first transport jets carrying Army troops into Saudi Arabia during the Persian Gulf War’s Desert Shield operation.

“In my mid-20s, I was commanding multimillion-dollar aircraft and experienced aircrews on classified missions all over the world,” Taiclet told the National Association of Real Estate Investment Trusts’ magazine.

In a statement published Monday, Taiclet lauded his predecessor’s performance and said his military service prepared him for the job.

“While serving on Lockheed Martin’s board, I’ve not only been impressed by the company’s continued growth as a leader in aerospace & defense but also by the dedication and commitment of Marillyn and Lockheed Martin employees to deliver for its customers,” Taiclet wrote. “As a military veteran, I understand the mission of this great company to provide global security and innovative solutions for the brave men and women who protect our freedom.”

After the CEO role changes hands, Hewson will remain executive chair of the board. Also on Monday, Lockheed promoted Frank St. John, previously the company’s head of Rotary and Mission Systems, to chief operating officer. Stephanie Hill succeeds him as head of RMS.

“The timing is right not only for our company, but for me personally,” Hewson wrote in a statement published Monday. “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. The future for all of us is bright.”