Sec. Ash Carter [0] did some really good work at reforming the pentagon, especially acquisitions, both as Deputy SecDef and later returning as SecDef. He also served as Under Secretary for Acquisitions (AT&L)
Sec. David Norquist [1] was another Deputy SecDef who helped reign in DoD costs. He also served as Comptroller before DepSecDef. There was whispers that he did actually fire people for wasting DoD funds.