For several years Norwegian firm DSG has been developing a breakthrough bullet design that enables bullets to use supercavitation when in the water to travel farther than two meters (six feet) at high enough speeds to actually hurt people. DSG has finally perfected its CAV-X Supercavitating Ammunition that is effective at up to 45 meters underwater. U.S. SOCOM (Special Operations Command) now plans to adopt the CAV-X for use by its special operations troops, particularly the U.S. Navy SEALs.
There are two variants of CAV-X; A2 which can be fired from outside water at targets in the water and X2 which is optimized to work when fired underwater. CAV-X can be fired from the rifles already carried by SOCOM personnel. The CAV-X is still in development with the supercavitating being optimized for range, accuracy and wounding capability. Current designs work, but tweaking the design has shown there is room for improvement through further modifications.
CAV-X fills a need because traditional bullet designs do not get very far in water. Most pistol bullets, when fired underwater, become harmless (to people) after going through about 600mm (two feet) of water and lose all momentum after going about five meters (15 feet). When fired from close to the surface (from a dock or ship) bullets pick up a lot of speed before hitting the water and will hurt someone up to about three meters (10 feet) underwater for a rifle and half that for most pistols.
The DSG bullet uses a shape designed to create an air bubble (supercavitating) around the bullet by utilizing the gases generated by the bullet propellant. This enables the supercavitating bullet to travel much more efficiently underwater. The DSG bullets are also balanced to enhance the supercavitating duration.
The first generation CAV-X 5.56mm rifle bullet was effective at up to 14 meters under water while larger bullets like the 7.62mm was effective up to 22 meters and the 12.7mm (.50 caliber) was good out to 60 meters once entering the water after being fired from the deck of a ship. The latest generation of CAV-X doubles those effective ranges in most cases. The A2 version of the 7.62mm and 12.6mm bullets employed on boats and ships for defense against boats can now be effective against underwater swimmers.
There is a market for these bullets because of concern about terrorists using underwater swimmers to plant bombs or simply to reach a heavily guarded area. Thus ships that have 12.7mm machine-guns for defense against small boats can use these weapons, which are effective out to 2,000 meters in the atmosphere, to hit underwater swimmers that are close enough to the surface.
There have been earlier attempts to develop projectiles with better underwater range for combat divers to use. For a while during the Cold War, especially in the 1970s, the Soviet Union and the United States (with a lot of help from West Germany) came up with some more effective underwater weapons usable while underwater. These weapons fired heavier bullets that created an air bubble around them (supercavitating) which enabled them to maintain higher speeds for longer distances. These projectiles could hurt you out to about a 30 meters (a hundred feet). Beyond that, most of the time, you can't make out a target. The Russians still have their underwater "nail gun" (as underwater warriors call this type of weapon), in both pistol and assault rifle (it looks like a bulked up AK-47) forms. The U.S. still arms underwater troops with a similar pistol. And then there's also the speargun. It's used for hunting fish, is a one-shot affair, and has a range of about 4-8 meters (14-24 feet).
Meanwhile, British, U.S. and Israeli firms have developed special sonar systems for detecting divers. These devices are about the size of a barrel and will detect swimmers within at least an 800 meter radius. The diver detectors can be linked to automatic ASG (underwater grenades) dispensers that will electronically set the depth, then release the ASGs which act like depth charges. Divers can't swim deeper than 30 meters, because most ships are not that deep in the water. Even the largest supertanker has a draft of less than 20 meters. Combining sensors like ASG with the new DSG bullets greatly enhances protection for ships in the harbor.