The U.S. Navy is energetically, and at great expense, developing a revolutionary  next generation  warship weapon; the rail gun. Instead of using explosives to propel a shell out of a gun barrel, a rail gun uses magnetism to speed a projectile along two rails. This requires a lot of electricity, and for that reason, the new class of surface warships (DD-X and CG-X) are being built with sufficient electrical generating capacity to support a rail gun. While rail guns have been working in labs for years, it will be another 5-10 years before they will be ready for installation on a working warship. But when the rail gun does become reliable enough for this, it will be an awesome weapon. Generating six to 30 times the energy of current five inch (127mm) naval shells. The rail gun darts will travel at about 1.5 kilometers a second, to a range of of to 450 kilometers (depending on the amount of energy applied to the rails). When  the dart hits the ground, after spending up to five minutes in flight, it would bury itself 40 feet down, and leave a crater ten feet wide and ten feet deep. If the dart hits a tank, the vehicle is destroyed. A DD-X could carry 10,000 of these 127mm, 44 pound guided darts in the space now allocated for 1,500 110 pound 127mm shells and their propellant charges, and fire them at the rate of six a minute. One of the things slowing down introduction of rail guns is a guidance system that can survive the high acceleration of the dart (from sitting still to over 5,000 kilometers an hour in a second or two.) U.S. weapons researchers have built guidance systems, at great expense,  that can operate in a conventional artillery shell. But the rail gun projectile is moving more than twice as fast. Moreover, these 44 pound, 127mm guided darts will be expensive, costing up to $5-10,000 each. That means a DD-X could be carrying $100 million worth of munitions for its rail gun. However, the navy feels that the rail gun will provide weapons that are cheaper than missiles, but still have the long range and accuracy that missiles possess.