Control of the air is the most important thing in war.
Britain has many hi-tech flying machines, like the Harrier jump-jet, which can take off and land vertically.
It also has a large number of troop-carrying helicopters and fighter planes.
The US Airforce is the most powerful in the world. It has a huge amount of fighters, bombers, helicopters, refuelling planes and many more.
This means that its troops on the ground have a big advantage, because the planes can quickly give them support if they need it.
Some of the most important planes the US has are called Stealth Bombers. These can't be picked up by Iraqi radar, making it very difficult to stop them.
Iraq has about 180 planes that are good enough to take on the USA and UK. But only 90 of these work.
Its pilots don't have much experience because "no-fly zones" over their country have stopped them practising.
Andrew Brookes, an air specialist at the International Institute for Strategic Studies in London, described Iraq's defences against air attacks as "rubbish".