“Hooah!” is a slang phrase used by members of the US military, and although its exact origins are not clear, it is typically thought to come from the acronym HUA, which stands for for “heard, understood, acknowledged.” The phrase is generally used in response to a statement or order from a military superior. “Hooah!” also is often used by members of the US military as a morale-boosting cheer, and its broad definition has even been described as meaning “everything and anything but no.”
More about the US military:
In 2011, the US military had about 1.1 million soldiers and more than 400,000 civilian and military employees, so if it were a city, its population would make it the sixth-largest city in the US.
Only one out of every four Americans age 17 to 23 are thought to qualify for military service.
It takes more than 22 gallons (83.3 liters) of fuel to support each US soldier for one day on the battlefield. By comparison, during World War II, it took 1 gallon (3.8 liters) of fuel for each soldier.