Troops already are facing force reductions, and the Army alone has announced plans to trim its ranks by 80,000 over the next five years.
Officials agree that the military has undergone cycles of expanding and shrinking of the force over generations. Hagel said this time is different, and worse, however, because of what he described as a "very dark cloud" of uncertainty hanging over the Pentagon as Congress considers whether to reverse $52 billion in spending cuts that are set to go into effect in 2014.
At the Naval Air Station in Jacksonville, Fla., Hagel told an estimated 100 civilians gathered in a bustling jet maintenance hangar that the military had not been prepared for the $37 billion in cuts that took effect this year, forcing the furloughs. While he said he was deeply sorry for the strain the crunch has put on families, he said he would not slash troops' training or other readiness budgets any further to prevent huge gaps in national security.
"I'm sure you realize how disruptive the furlough is to our productivity. So I'm hoping that we're not going to do it again next year," Elizabeth Nealin, a research and engineering manager at the navy base's fleet readiness center, told Hagel.
"Have you planned for a reduction in force?" Nealin asked bluntly.
Hagel said if the $52 billion cut remains in place, "there will be further cuts in personnel, make no mistake about that."
"I don't have any choice," he said.
The spending cuts this year may feel more dramatic than in times past because of a vast growth in Defense Department personnel and equipment costs over the past decade, said Todd Harrison, a senior fellow at the Center for Strategic and Budgetary Assessments in Washington. But current spending levels are close to what they were in 2007, when the war in Iraq was at its peak.