They've tried going to war against Afghanistan. They've tried zapping their enemies from unmanned CIA drones. They've even tried – without much success – some old-fashioned police spadework. Now the Americans have a new idea of how to wage their war on terrorism: giant hot-air balloons.

The Pentagon, which has encouraged the country's biggest defence contractors to submit tenders, wants to station dozens of helium-powered airships 20,000 metres above America's coasts to track missiles or hostile aircraft and to monitor what officials call "potential terrorist activities on the ground".

Airships are believed to be capable of providing photographs of quality up to 50 times greater than those from space satellites. According to yesterday's Los Angeles Times, they would not be armed initially, but would be designed to carry up to 2,000kg in "payload" – jargon for bombs and missiles. The plan is to send the blimps into the sky by 2010.