[No1_Charlie]

The AGSM consists of a deep intake of breath, followed by breath-holding and grunting for about three seconds, followed by an explosive exhalation and repetition of the process. This act increases the pressure inside the lungs and chest and, in effect, supercharges the blood pressure on the "inlet" side of the heart. With this technique, a well-trained pilot can raise his blood pressure around four Gs' worth.

Did pilots exercise this method in WWII?