Supercavitating Machine-Gun Bullets.

In 1957 a British Government White Paper proposed cutting funding to manned interceptor projects in favour of developing surface to air missile systems. As should have been obvious, but evidently was not, this was a very foolish decision. If in a total war footing it may be possible to destroy any aircraft entering your airspace with missiles. In most other situations it is prudent to intercept and confirm that a target is in fact hostile. Much of the cold war was spent with fighters intercepting intruding aircraft and driving them off, with never a shot fired. Such actions are of course impossible for a missile.
A similar situation occurs with naval operations. A modern warship or submarine can destroy a target at hundreds of miles range, but more commonly a target needs to be visually verified. It may need to be boarded and searched to confirm it is what it seems. If it is hostile, a captured vessel will yield more useful intelligence than one that is sunk. If shots need to be exchanged, it will often be a warning shot or a burst to disable the engines. Large calibre shells and missiles are not suited to such tasks. For these reasons the machine gun is an important but often overlooked weapon for naval operations, be it mounted on boat, helicopter or warship.
Last night, while researching some information on supercavitating torpedoes I came across some references to supercavitating bullets. I came across the idea of applying supercavitation to rifle calibre bullets a few years ago in the context of deep penetration rounds for big game hunting. When supercavitation features are applied to bullets they also have an extended range when fired into the water. For example, the 30mm cannon round being developed has a through-water range against mines of at least 75 feet.

Supercavitating rounds of smaller calibres have also been developed and have an obvious application for naval machine guns. With a longer underwater range machineguns can be used for the destruction of underwater mines and have a better capability against enemy frogmen. There has been some suggestions that such weapons can be used against torpedoes. By the time a torpedo gets into machine gun range things will be pretty desperate so there is nothing lost in trying this by then I suppose. In larger (cannon) calibres supercavitating rounds may have a more practical application against torpedoes if a ship’s CIWS system can be programmed to also engage underwater targets.
There are a couple of things I wonder about supercavitating machine gun ammo. Would the rounds have an acceptable performance through air at likely engagement ranges? Many of the targets likely to be engaged by naval machine guns will be of wooden planking or sheet metal, so does the round have adequate penetration against these? If the answers to these questions of performance are positive these rounds is we may see small calibre supercavitating rounds adopted more widely for naval service.