Along with other such intelligence-gathering aircraft, the Rivet Joint is characterised as "low-density, high-demand" - or as the commander of the US Air Combat Command's 55th Wing put it: "That means we don't have a lot of planes but we're busy."

There are 16 of them, operating normally from Nebraska in the USA, Japan, England and Crete. They were used extensively during Nato operations in Bosnia and Kosovo.

Providing sufficient planes for the Kosovo operation involved shutting down Operation Northern Watch - the enforcement of the no-fly zone over northern Iraq - for several days.

As with so much military equipment, a whole series of upgrades is ongoing to enhance its capabilities in detection and in communicating with other surveillance aircraft such as Joint Stars and AWACS, and with strike aircraft that are called in to attack targets it identifies.