Missions too dangerous for manned aircraft include everything from probing enemy air defences to carrying out surveillance over territory where a shot-down pilot could be used as a hostage.

Many of the sites are protected, and any operation would have to suppress at least part of Iran's air defences, and all its missiles and naval power, to limit any retaliation.

One night in April, as the capital's air defences blazed wildly into the night sky, the flying Tigers dropped bombs on a gas installation and an air force base.