5922976 ?Amid bursting ?crumps? with trench mortar ready, Seaforths watch through periscope for the Bosch? (b/w photo) by Unknown photographer, (20th century); National Army Museum, London; (add.info.: ?Seaforth Highlanders watch through a periscope as their trench mortars fire a salvo?, 1915 circa. Photograph, World War One, Western Front, 1915 circa. A mortar is essentially a short tube designed to fire a projectile at a steep angle so that it falls straight down on the enemy. Such weapons were ideally suited for trench warfare, especially where the lines of the combatants were very close together. As this image demonstrates, mortars could also be fired from the relative safety of the trench. From a collection of one hundred and one stereoscopic photographs entitled ?The Great War? including the official series.); by National Army Museum ; out of copyright.