Sarah P. Mather receives a U.S. patent on April 16, 1845 for her “Submarine Telescope and Lamp,” the earliest known patented underwater telescope/periscope-like device.
On April 16, 1845, Sarah P. Mather of Brooklyn, New York, received U.S. Patent No. 3,755 (commonly cited in later retellings as No. 3,995 or 3,389) for her invention titled a "Submarine Telescope and Lamp."[1][3][16] This device was designed as an "apparatus for examining objects under the surface of the water," allowing observers to visually inspect submerged hulls, obstructions, and other underwater features from above the surface.
Mather’s apparatus combined a watertight tube with a lamp and optical elements so that light could be directed into the water and reflected back to a telescope or viewing lens. In the mid‑19th century, this was a radical improvement over the usual practice of sending divers or dry‑docking ships to check for damage. Her design is widely described in modern historiography as the first documented underwater telescope and an early periscope‑like instrument, making it a pioneering step toward later submarine periscopes and underwater inspection technologies.[1][3][9][12]
The patent was also historically significant from a gender perspective. In an era when very few women in the United States obtained patents—especially for technical devices related to navigation, optics, or engineering—Mather stands out as one of the earliest American women to be granted a patent for a scientific instrument. Her success required engaging with legal and bureaucratic systems that were implicitly structured around male inventors, overcoming social expectations that discouraged women from mechanical experimentation and commercial invention.
Issued at a time of expanding naval and commercial fleets, Mather’s invention contributed to the evolving toolkit for maritime safety. Later commentators have linked its relevance to both the Mexican‑American War period and, more importantly, to Civil War‑era naval operations, where underwater observation and detection of hazards became critical.[3][16] The April 16, 1845 patent grant thus marks a milestone in women’s history in science and engineering, and in the technological lineage of underwater viewing devices and periscopes.