page_title: Depression range finder
hierarchical_section_title: Depression range finder
caption_attribution_description: English: This photo, taken in August, 2010, looks northwesterly and shows three concrete columns that used to serve as the bases for depression position finder (DPF) instruments that were used by the U.S. Coast Artillery to control the fire of their gun batteries. These three columns were part of the fire control system at Fort Warren on Georges Island in Boston Harbor. They are located atop Bastion E in the southwest corner of the fort. The two nearest columns were enclosed in one fire control building and the one in the background was in a separate building. Originally, a floor existed at a level that would have put the roughly four foot-tall instrument at the user's eye level. The roofs, floors, and walls of these buildings, built in the period 1905-1920, have since collapsed and disappeared. The barrel-shaped building behind the second column is an old magazine, likely left over from the time when powder for muzzle-loading cannon was stored in this area.
context_page_description: The depression range finder was a fire control device used to observe the target's range and bearing to calculate firing solutions when gun laying in coastal artillery. It was the main component of a vertical base rangefinding system. It was necessitated by the introduction of rifled artillery from the mid-19th century onwards, which had much greater ranges than the old smoothbore weapons and were consequently more difficult to aim accurately. The DRF was invented by Captain H.S.S. Watkin of the Royal Artillery in the 1870s and was adopted in 1881. It could provide both range and bearing information on a target. The device's inventor also developed a family of similar devices, among them the position finder, which used two telescopes as a horizontal base rangefinding system, around the same time; some of these were called electric position finders. Some position finders retained a depression range finding capability; some of these were called depression position finders. Watkin's family of devices were deployed in position finding cells, a type of fire control tower, often in configurations that allowed both horizontal base and vertical base rangefinding.
context_section_description: The depression range finder (DRF) was a fire control device used to observe the target's range and bearing to calculate firing solutions when gun laying in coastal artillery. It was the main component of a vertical base rangefinding system. It was necessitated by the introduction of rifled artillery from the mid-19th century onwards, which had much greater ranges than the old smoothbore weapons and were consequently more difficult to aim accurately. The DRF was invented by Captain H.S.S. Watkin of the Royal Artillery in the 1870s and was adopted in 1881. It could provide both range and bearing information on a target. The device's inventor also developed a family of similar devices, among them the position finder, which used two telescopes as a horizontal base rangefinding system, around the same time; some of these were called electric position finders. Some position finders retained a depression range finding capability; some of these were called depression position finders. Watkin's family of devices were deployed in position finding cells, a type of fire control tower, often in configurations that allowed both horizontal base and vertical base rangefinding. Watkin's system included automatic electrical updating of range and bearing dials near the guns as the position finders were manipulated, and a system of remotely firing the guns electrically from the position finding cell. The improved system was trialled in 1885 and widely deployed in the 1890s. Functionally equivalent devices were developed for the United States Army Coast Artillery Corps and its predecessors, called depression position finders or azimuth instruments depending on function (vertical base or horizontal base), adopted in 1896 and deployed widely beginning in the early 1900s as the Endicott program of modern coastal defences was built. These devices were also used by both countries to control submarine (underwater) minefields.
caption: The remains of three American base end stations with their concrete DPF mounting columns. These columns date to about 1910.
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