Super-loudhailers are becoming louder still

YOU NEEDLRAD a pretty powerful bullhorn to broadcast a message to someone who is 2km away. But that is what America’s navy is currently looking for. It wants, among other things, to be able to warn the crews of small vessels, who may or may not be hostile, not to come too close to its ships. And, if the warning is ignored, it would like to be able to hit them with a noise so piercing and horrible that even a determined attacker would have difficulty ignoring it and carrying on regardless.To some extent, it can do this already. After , a guided-missile destroyer, was attacked successfully by boat-borne suicide-bombers in 2000, ripping a huge hole in the vessel’s side (see picture) and killing 17 sailors, America’s admirals have been understandably nervous about the proximity of such craft. One consequence of that nervousness is that they have acquired so-called Long Range Acoustic Devices (s) to hail possible threats. The current top of the range, the 2000RX, generates 160 decibels, while a portable cousin, the 100X, manages 137. But the navy now wants something that combines the former’s power with the latter’s convenience, and with a higher fidelity of transmission.