Spending on third offset tech growing rapidly.

* The Defense Department is pumping money into so-called third offset technologies intended to help the U.S. military maintain its technological edge.

Between fiscal years 2011 and 2015, the Pentagon spent $27.8 billion on the portfolio, according to a recent report by analytics firm Govini. The Defense Department estimates that it will spend about $18 billion on the initiative over the next five years.

The third offset "constitutes a massive overhaul in U.S. military operating concepts and technological investments," the report said.

There is no official third offset spending account in the Defense Department budget, so classifying particular items as such can be a subjective exercise.

Govini grouped the technologies into five categories: target tracking; navigation and guidance systems; conventional long-range missiles; directed energy; and hypersonics.

Between fiscal years 2011 and 2015, spending on hypersonic technologies saw the largest relative growth, increasing by a whopping 98 percent to a total of about $200 million, the report said.

Hypervelocity projectiles (HVP) can travel at a speed of Mach 3 or faster. They can be fired from an electromagnetic rail gun or conventional 5-inch guns on combat ships.

"One advantage of the HVP/5-inch gun concept is that the 5-inch guns are already installed on Navy cruisers and destroyers, creating a potential for rapidly proliferating" hypersonic weapons across the force, naval analyst Ronald O'Rourke said in a recent Congressional Research Service report.

Pentagon leaders have identified hypersonics as a promising area for future investment.

"The spending trends... will continue their steep climb, especially as the...