Even before the baby boom generation retires and begins using expensive Social Security and medical programs, the Department of Defense is sorely underfunded, according to a report from The Heritage Foundation, a conservative Washington think tank.

Pentagon needs for everything from missile defense to combat operations, from procurement of weapons systems to personnel costs, require spending at a minimum something like the equivalent of 4 percent of gross domestic product, according to the 32-page report.

But funding for the military forces lags far behind that level at 3.2 percent, according to Heritage defense experts.

"Congress would do well … to sustain national defense budgets at 4 percent of GDP," the report recommends.

It is titled "Four Percent for Freedom: The Need to Invest More in Defense" and was published last week by the foundation.