John Louis Lay (1832–1899) was an American inventor of the spar torpedo. He was born in Buffalo, N. Y. During the War of the Rebellion he was appointed a second assistant engineer in the navy in July 1862. In 1864 he invented the torpedo with which Lieutenant Cushing sank the Confederate armor-clad ram Albemarle. After the Confederates abandoned Richmond, he assisted in clearing the James River of obstructions which were impeding the advance of Admiral Porter's fleet.

Following the end of the conflict, he resigned his position and traveled to Peru in South America, where he was employed in mining the harbor at Callao as a defense against an expected attack by the Spanish fleet. After he returned to the United States in 1867 he perfected the Lay dirigible submarine torpedo, which he sold to the Federal government. The torpedo was used by Peru during the War of the Pacific, but it wasn't successful.

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