WW I English: British Vickers machine gun crew wearing PH-type anti-gas helmets. Near Ovillers during the Battle of the Somme, July 1916. The gunner is wearing a padded waistcoat, enabling him to carry the machine gun barrel. See Image:Vickers machine gun crew with gas masks rear view.jpg for an alternate view of this crew. File:Vickers machine gun crew with gas masks.jpg Public Domain
This photo demonstrates the often monstrous sizes of WW1 guns aiming to hurl huge projectiles as far as 25 miles. This one is most likely a coastal gun, its breach being calibrated by technicians. Firing these monsters required the crew to stay well clear of the gun -- as far as 50 meters from the breach -- and fire it by a pull cable. The resulting blast easily blinded those uncaring ones who insisted on looking. The force of the combustion required re-sighting the gun after every shot.