St. LOUIS — A recent visit to St. Louis highlights one challenge Secretary of Defense Ash Carter faces as he attempts to tap outside cultures of innovation: striking the balance between old and new.

Carter was in town Sept. 9 for a DARPA conference, dubbed "Wait, What?" which brought in 1,200 researchers to discuss new advances in technology. About half of those had never worked with DARPA before, according to Pentagon figures.

The secretary, with a reputation as a technologist, took the stage for a keynote address to hoots, whistles and a standing ovation from the crowd, in a scene that would not be out of place at an Apple keynote address.

"You're some of our nation's most innovative physicists, chemists and geneticists; nanotechnologists, molecular biologists, data scientists, computer scientists, neuroscientists; experts in manufacturing, cyber, satellites and space," Carter told the audience. "With all of you in this one building, the opportunities for cross-collaboration are endless."

But at the same time, Carter spent the morning paying homage to one of the Pentagon's oldest technological innovators in Boeing.

The secretary was given a briefing on the company's innovative — and secretive — "Black Diamond" manufacturing plan, and got an early look at both Boeing's T-X trainer design and a new configuration for the F-15, which will allow the fighter to carry 16 air-to-air weapons.

"We've been talking about innovation in technology, new things, new products, new concepts; innovation in manufacturing, which is breathtaking and also very consequential; and innovation in how we attract and develop wonderful people like you," Carter told a group of Boeing employees in comments at the end of his visit.

Much of Carter's first few months in office have been focused on bringing in outside voices to the department, including the creation of a DoD outpost in the heart of Silicon Valley. With all the focus on newer companies, it would be understandable if some who work for the traditional primes felt a little left out.

That issue was hinted at when a Boeing employee asked whether the focus on Silicon Valley means traditional primes are being left behind. Carter acknowledged that "Boeing doesn't get all the attention in the newspapers, but I do think, and this is important, that you do get attention in a different way," namely, because in the fact they are a well-known defense firm.

Asked by a reporter after the DARPA event if he worries about "blowback" from the traditional defense industry over his outreach to new companies, Carter quickly noted that "'old companies' doesn't mean 'non-innovative companies.'"

"It's not an either/or," he added, emphasizing Boeing's innovation as particularly important in the manufacturing sector. "We need all of these channels of innovation to stay the best."

Twitter: @AaronMehta