The 3-inch gun M1903 and its predecessors the M1898 and M1902 were rapid fire breech-loading artillery guns with a 360-degree traverse. In some references they are called "15-pounders" due to their projectile weight. They were originally emplaced from 1899 to 1917 and served until shortly after World War II. These 3-inch guns were placed to provide fire to protect underwater mines and nets against minesweepers, and also to protect against motor torpedo boats. In some documentation they are called "mine defense guns". The 3-inch guns were mounted on pedestal mounts that bolted into a concrete emplacement that provided cover and safety for the gun's crew.

Several boards have been appointed by US presidents or Congress to evaluate the US defensive fortifications, primarily coastal defenses near strategically important harbors on the US shores, its territories, and its protectorates.