The Aberdeen chronograph was the first portable gun chronograph, an instrument for measuring the muzzle velocity and striking power of a projectile fired by a gun. It was invented in 1918 by Alfred Lee Loomis at the U.S. Army's Aberdeen Proving Ground.^[1]

The method prevalent at the time was the Boulengé chronograph, which relied on the projectile passing through two wire screens. Breaking the first screen would release a rod held by electromagnets. While the rod was free-falling, breaking the second screen would activate a knife that marked the rod.^[2]

Loomis' chronograph had a drum rotating at constant speed with a tape spooled inside. The projectile would pass through two screens, breaking the insulation between metal plates and creating a short circuit. This created a spark that left two visible marks on the tape and measuring the distance between these marks would give the speed of the projectile.^[2][3] This method made it easier to measure the speed of larger shells and aircraft catapults.^[4][2] Loomis was issued a patent in 1921 for his chronograph.^[5]

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