A device which can be used as a sonic weapon is being deployed in London for the Olympics.
The American-built long range acoustic device (LRAD) can be used both as a high-powered loud speaker and to emit an ear-piercing beam of sound.
The Ministry of Defence confirmed that it was among a "broad range of assets" being used by the armed forces to provide security during the Games.
A spokesman said it would be used primarily in "loud hailer mode" in order to issue verbal warnings to any boats on the River Thames that were causing concern.
However the LRAD, which can reportedly emit a highly directional beam of sound at a pain-inducing 150 decibels, has also been used by the US Army as a crowd control device in Iraq.
"As part of the military contribution to the police-led security effort to ensure a safe and secure games, a broad range of assets and equipment is being used by our armed forces," the MoD spokesman said.
"This includes the LRAD which will be deployed during the Olympic Games primarily to be used in the loud hailer mode as part of the measures to achieve a maritime stop on the Thames."