U.S. Defense Department Christine Fox will serve as deputy defense secretary until a permanent deputy is confirmed by the Senate.

President Barack Obama appointed Christine Fox as acting deputy defense secretary Tuesday, making the civilian analyst — who inspired Kelly McGillis' character in "Top Gun" — the highest-ranking woman ever at the Pentagon.

Fox replaces Ashton Carter, who is stepping down Wednesday. Fox, who had been director of cost controls at the Pentagon before she left for the academic world over the summer, has remained an unpaid consultant to Carter since then.

Defense Secretary Chuck Hagel said Fox would serve "pending the nomination and confirmation of a permanent successor" as his top deputy — an acknowledgment that Senate Republicans could stall the permanent nomination over the so-called nuclear option, the new rules put in place by Democrats to speed up approval of judicial appointments.

In a statement, Hagel called Fox "a brilliant defense thinker and proven manager" who "knows the intricacies of the Department's budget, programs and global operations better than anyone."

A senior defense official told NBC News that Fox would be able to "hit the ground running like no one else can."

"Simply put, no one knows the issues as well as Christine," the official said.

Fox may be better known to the public as the model for Charlotte "Charlie" Blackwood, the civilian flight instructor who catches Tom Cruise's eye in the 1986 movie "Top Gun." Fox, former president of the Center for Naval Analysis, helped McGillis prepare for the role.>

Fox told People magazine in 1985, as the movie was in production, that she herself wasn't a fighter pilot but that she worked closely with them as a specialist in air and maritime defense.

"I don't know anything about flying airplanes, but I know a lot about the guy in the back seat — his mission, his radar and his missiles," she said at the time.

Courtney Kube of NBC News contributed to this report.

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