U.S. Defense Secretary Chuck Hagel has asked Mark Lippert to be his new chief of staff. Secretary Hagel told his top staff and uniformed officers that he'd picked Mark Lippert to be his new right-hand man in a series of changes in the front office and beyond as he settles into the job and builds his inner circle.

Lippert is now the Pentagon's Assistant Secretary of Defense for Asian and Pacific security affairs and will become chief of staff - in Pentagon-speak, the Special Assistant, or TSA - starting May 1. Marcel Lettre, the former deputy chief of staff who has been serving as acting chief since Hagel arrived Feb. 27, will be given another top job inside the Pentagon. But what job is as yet unclear.

Hagel also announced that Michael Lumpkin will be appointed as his Special Assistant with a "particular emphasis" on personnel and readiness issues starting in early May. Lumpkin had served as the acting Assistant Secretary of Defense for Special Operations/Low-Intensity Conflict and also as deputy chief of staff for operations at the Department of Veterans Affairs and served on active duty with the U.S. Navy for 21 years.

The new TSA will be the key to Hagel's success - selection of a special assistant is critical to the Defense Secretary's ability to get things done. Senior defense officials said Lippert has the background and experience to help Hagel navigate the Pentagon's bureaucratic waters and enforce Hagel's will across a building that has enjoyed unconstrained resources for more than a decade. The two men have known each other for many years. Before coming to the Pentagon, Lippert, a Navy reservist who served a year in Iraq between 2007 and 2008 as an intel officer with a SEAL team, worked for a string of senators on Capitol Hill - from Sen. Dianne Feinstein to Tom Daschle to Patrick Leahy before joining the Senate Appropriations Committee as a staffer. Then, in 2005, he became foreign policy adviser to Senator Barack Obama.

Observers suggest this is a good time to "rearrange some of the players on the field," now that he has cleared some of the hurdles he faced during his first two months as Secretary - the release of the budget, the beginning of the strategic review, the Article 60 assessment, and a trip to Afghanistan. Reaction to the choice in and outside of the building was positive.

Lippert is thought to be able to bring the kind of approach to Hagel's front office that it will need if it is to be effective. "Mark is results-oriented and collaborative and boils it down," a senior defense official has told media. "I think that is of significant value in the Pentagon, which is prone to bureaucracy." As Assistant Secretary of Defense, Lippert managed as many as 150 people, including four Deputy Assistant Secretaries of Defense. A successful chief of staff must be able to winnow what's important, determine who can handle what task, and tee up decisions that need to be made at the secretary's level, according to those familiar with front-office operations. For the TSA, the task is simple:"Winnow and tee."

Observers say that Hagel is clear and direct, a quality appreciated by the take-that-hill culture of the uniformed military -- he has a "remarkable ability to cut to the heart of the matter," said one official. "He'll zero in on the one data point in a five-page PowerPoint presentation and dig in on the question that's most important. He's really signalled to the building that he wants speed, he doesn't want a lot of fluff, and he wants his questions answered."

Lippert's replacement, for now, will be Peter Lavoy, now a Principal Deputy Assistant Secretary of Defense working on Afghanistan, Pakistan,India and Central Asian policy, to serve in an acting capacity as the assistant secretary of defense for Asia and Pacific security affairs.

Leon Panetta's Special Assistant, Jeremy Bash, who has been serving in an advisory role for the last several weeks, is leaving the building today. Bash, who is likely to have a number of career options after directly working for the former Defense Secretary, has not yet announced where he's headed.

This report is drawn from information published by Situation Report