Speculation is mounting of a US strike on Iran as military resources are deployed into position.
More than 40 extra jets are said to have been sent to the UK and Europe by Donald Trump in recent days.
They are thought to include stealth bombers and air-to-air refuellers - which could be critical for any operation in the Middle East.
The movements have raised expectations that action is imminent, after Mr Trump denied he was interested in securing a ceasefire between Israel and Iran and told residents to evacuate Tehran.
Instead he has stressed the importance of stopping Iran from getting nuclear weapons, and cut short his attendance at the G7 summit in Canada to return to Washington.
