Water has long been used by law enforcement around the world as a non-lethal weapon in crowd control. High-pressure water hoses can suppress angry mobs with hundreds of people in a matter of seconds.
Consider the principle of taking a non-lethal water weapon and "turning it up a bit" to adapt it into a design capable of delivering enough punch to make it combat-worthy. This was the starting point for the U.S. military's initial deliberations in the design of what it's now calling hydro-ordnance.
The scope of the design was eventually expanded to include mortar rounds, anti-tank weaponry and aerial smart munitions. The ultimate goal is an inexpensive, environmentally-benign ammunition that has the same lethality and effectiveness as traditional munitions in use today. With the latest and most advanced hydro-ordnance to date, U.S. military researchers believe they have reached that goal, and will be able to deploy it across the entire military infrastructure.
Dr. Blanchard suggests:
In order for this initiative to effectively reduce the cost of military spending on ammunition, we had to redefine the idea of "the round" across the board. We would like to see water based munitions replace traditional ore- and alloy-based munitions in the next 15 to 20 years. The pace of this replacement will be gradual and consistent with our commitment to national security. If our projections are correct, based on some of the design options we've been presented with, the successful development of a water round could reduce spending by up to 80 percent.
The picture below shows Srgt. Max Moore test firing the pump action CPS 1200 Lance. This will replace the AR-15 as the standard issue rifle for U.S. Infantry.