On March 21, the United States entered its third “unexpected” war in less than a decade. President Obama announced that, while the U.S. would initially take the lead role in the Libyan operation, we would quickly turn over operations to other powers.

Still, the White House acknowledged that the operation could not have gotten off the ground without American military might. Only our armed forces could do the heavy lifting—grounding Gaddafi’s air force and turning back land assaults on the rebels. This hard fact should serve as a reality check for any impulse to gut the Pentagon budget, regardless of where you stand on the appropriateness of this particular mission.

Recently my colleagues at The Heritage Foundation undertook an important exercise. The Heritage team identified, one after another, all the vital national security interests of the United States. These are the military missions where failure is not an option and “soft power” (diplomacy or what have you) can’t substitute military force in controlling ground, air, sea, cyberspace, and outer space. They considered five different regions: Asia, Europe, the Middle East, the American homeland, and space. Then they identified the military assets required to support our vital interests in each domain—and the assets on hand.

In determining vital interests, our analysts invented nothing. They just looked at authoritative work already done by others. They drew heavily from work done by the Obama administration (including the 2010 Quadrennial Defense Review) and by a commission chartered by the Democrat-controlled Congress, which issued the QDR Independent Review Panel Report.

The Heritage team used the same analytical methods used by Pentagon planners and the congressional Armed Services Committees to determine America’s defense needs. This allowed them to lay out: the current and significant emerging challenges to U.S. security; the current and future military capabilities required to address these challenges, and the cost of maintaining those capabilities over the next five years.

They determined the budget for this force by totaling: current projected budgets; the Congressional Budget Office’s assessment of shortfalls; funds required to “reset” equipment after operations in Afghanistan and Iraq; efficiencies that can be gained in operations, logistics and personnel; and modernization costs.

The analysis concluded that, to serve all vital national security interests, the core defense budget would need to average about $720 billion annually over the five year, FY 2012-FY2016 period.

That’s substantially more than the president’s budget proposes, but it’s the reality of what is needed. And by the way, this analysis assumes the Pentagon can achieve some significant efficiencies—particular in manpower and logistics costs. Nobody can claim there is not money to be saved from within the defense budget through eliminating waste, undertaking reforms, and increasing efficiencies. But those savings, the study argues, should be reprioritized so the military can best decide where to focus scarce funds on the need to reset equipment used in war and buy new systems in order to retire the old ones.

It is irresponsible to give tomorrow’s soldier yesterday’s equipment. But that’s what our government is currently doing. The Air Force inventory is older than it has been since the inception of that Service in 1947. The Navy is the smallest it has been since 1916. The Army needs to replace most of its vehicles. 

In fact, the cost of recapitalizing the force is as high as it is now precisely because past Congresses systematically and deliberately underfunded procurement and modernization. The bill is not coming due, and will grow bigger and bigger the longer Congress tries to avoid its Constitutional responsibilities.

Those waving budget axes on the Hill argue that we can serve all vital interests with a smaller force and a different strategy. It’s an appealing sound bite, but where’s the proof?  The burden is on them to demonstrate how they can accomplish everything expected with less—and without increasing risks to levels previously considered unacceptable. 

Defense is not just another line item in the federal budget. At a time when our federal government has assumed responsibilities that are constitutionally beyond its reach (and, in some instances, quite probably unconstitutional), it is important to remember that Washington’s primary and constitutionally mandated obligation is to keep Americans safe. The Preamble of the Constitution says the purpose of government is to “provide for the common defense.” This is an obligation morally different from and superior to any other held by the federal government.

Even more fundamentally, failing to prepare for threats will not make the threats go away. In fact, it is the surest way to guarantee that they will manifest themselves, because the primary purpose of American power is not to win conflicts but to deter them. As Ronald Reagan was fond of saying, “of the four wars that occurred in my lifetime, none happened because America was too strong.”

Jim Talent is a Distinguished Fellow specializing in defense studies at The Heritage Foundation.