By RUSTY DENNEN

Within about a decade, the Navy envisions fitting ships with a super weapon powered not by explosives, but by electromagnetic energy.

If all goes as planned, the Office of Naval Research said Tuesday, an electromagnetic railgun would fire a 40-pound inert projectile up to 115 miles--able to take out a missile, enemy ship, or target on land--by kinetic energy alone. No explosives would be required.

Tests have begun on a prototype launcher developed by BAE Systems Inc. The Navy marked the milestone by holding a press conference on the latest developments with the project, which began in 2005.

"The BAE prototype represents a significant step beyond previous laboratory-style launchers" that have been used until now, said Roger Ellis, who manages the railgun program for ONR's Naval Air Warfare and Weapons Department.

The prototypes, Ellis said, "are closer to what we would want to put on a ship someday." The purpose of the tests is to evaluate the barrel life and structural integrity of the launcher.

A second prototype, developed by General Atomics, will undergo tests in coming months.

Dahlgren's firing range has been the site of several tests so far, including a 32-megajoule shot in December 2010--a record for an electromagnetic pulse. A megajoule is the energy equivalent of a one-ton truck traveling at 100 mph.

The concept of a railgun is simple, first envisioned in the 1860s when electromagnetic field theory was developed: A pulse of electricity traveling along two parallel rails propels a projectile at up to 5,600 mph.

The launchers under development by BAE Systems and General Atomics are just one component. The gun must be small enough to fit on a ship, yet powerful enough to deliver the million-plus ampere jolt to fire a projectile way beyond the range of current Navy guns.

That will require an advanced battery power system and the ability to hit a moving target at a great distance.

Ellis said the technology to accomplish those goals is being developed in phases. The overall aim is to have a railgun on a ship as early as 2025. It would fire 10 rounds per minute.

The five-inch guns currently on Navy ships have a range of about 15 miles, and can fire 20 rounds per minute.