Prone
Prone position, a posture in which the body is completely supported by gravity and secured against falling and sliding by a firm surface.
The illustration shows Lamming Miniatures 20 mm British infantry who have adopted a prone firing position after lying down. Notice that the rifleman has adopted the perfect prone, unsupported firing position, with legs spread and heels flat against the ground, whereas the Bren gunner risks being hit in the heels. Furthermore, his balancing act on kneecaps and toes is extremely painful and makes precise shooting impossible.
Source: Pierer’s Universal-Lexikon 4. Auflage 1857–1865