4.2" Chemical Mortar Slide Rule

The National WWII Museum, 2006.252.001

Unlike a direct-fire weapon, which simply requires the gunner to place the target within his sights, a mortar requires a complex firing solution to be aimed accurately. The tube has to be pointed in the right direction, at the proper angle, with the correct amount of propellant, to hit the proper target. In the days before handheld electronic calculators, mortar crews were issued these slide rules, which allowed them to solve the firing equations quickly.