The footguards are the senior infantry regiments in the British army; most of the time, they train like other soldiers, a long way from London. Sometimes they may find themselves in war zones. In recent years they have also been sent to Bosnia and to Kosovo, to Iraq and Afghanistan in order to help with the international peace-keeping forces.
If you are planning to see it, be prepared. The whole process takes about 45 minutes and the crowds at the Palace are substantial.