In the United States military, flag officers are:
- Admirals and vice admirals in the Navy
- Generals and lieutenant generals in the Army and Air Force
- Generals, lieutenant generals, and major generals in the Marine Corps
In the United Kingdom, flag officers are:
- Admirals of the fleet, admirals, vice admirals, and rear admirals in the Royal Navy
- Generals, lieutenant generals, major generals, and brigadier generals in the British Army
- Air marshals, air chief marshals, air vice-marshals, and air commodores in the Royal Air Force
In other countries, the ranks of flag officers vary, but they typically include the following:
- Generals and lieutenant generals
- Admirals and vice admirals
- Air marshals and air chief marshals
Flag officers are typically responsible for commanding large military units, such as divisions, corps, or fleets. They may also serve in staff positions at the highest levels of the military.
The term "flag officer" comes from the fact that these officers are entitled to fly a flag from their ship or aircraft. This tradition dates back to the days when sailing ships were the primary means of naval warfare. The flags flown by flag officers were used to identify their ships and to signal their commands.
Today, the flags flown by flag officers are still used to identify their positions, but they are also used to symbolise their authority and leadership. Flag officers are the most senior members of the military, and they play a vital role in ensuring the security of their countries.