Vice Air Marshal S K Sonpar says,
A barrel roll is a basic aerobatics manoeuvre which was discovered by fighter pilots during the First World War. During a barrel roll, an airplane makes a complete rotation on its longitudinal axis while following a helical path (smooth curve) such that after the rotation, the jet maintains its original direction. The barrel roll is so named because an aircraft executing this manoeuvre looks as though it were flying with its wheels running along the inside edge of a barrel. To visualise a barrel roll, imagine an airplane trying to fly in a horizontal corkscrew around the line of the direction of travel. This move is not used by airplanes apart from fighter jets, but the Boeing 367-80 and Concorde prototype were barrel-rolled during testing. A barrel roll is hardly ever used in modern-day aerial combat, which are called ‘dog fights’. One is likely to see it being executed in air displays where it is demonstrated to show the handling characteristics of the fighter. It is also widely used in the training of fighter pilots as it enhances their confidence in the ability to control an aircraft.