He was responsible for the construction and repair of United States Navy ships during the American Civil War (1861–1865), as well as in the years immediately before and after it.

His British-born father was an architect who had emigrated to the United States in 1793 and from 1803 worked as Clerk of the Works and Principal Surveyor at the United States Capitol Building in Washington under Architect of the Capitol Benjamin Henry Latrobe, serving as the building's construction superintendent.

[6] He learned the trade of ship carpenter[6] and received training in Europe, visiting shipyards in the United Kingdom, France, Denmark, and the Russian Empire,[7] Around 1827, Lenthall became the apprentice of Samuel Humphreys; Humphreys had become Chief Constructor of the Navy in 1826 while retaining his position as the Naval Constructor at the Philadelphia Navy Yard in Philadelphia, Pennsylvania, where he continued to spend most of his time.

In the early 1840s he completed his efforts to refine the plans of the sailing frigate USS Raritan, laid down in 1820 but not launched until 1843, and she emerged as a speedy ship for her day.

[21] During his tenure as Chief Constructor, he handled the matter of the reconstruction of the sailing frigate USS Constellation of 1797, drydocked in 1853 in poor condition after languishing in ordinary at Gosport Navy Yard in Portsmouth, Virginia, since 1845.

[23] During his tenure as chief of the bureau he was responsible for the design of some of the most significant U.S. Navy ships constructed in the years just prior to the onset of the American Civil War.

[28] Pook and Eads in turn modified Lenthall's design to produce the first American ironclad warships, the seven City-class ironclad gunboats that served on rivers in what is now the central United States as the core of the U.S. Army's Western Gunboat Flotilla, later transferred to the U.S. Navy as the Mississippi River Squadron.

Built of poor materials and not completed until 1867, Dunderberg was unsuccessful and the U.S. Navy rejected her for service,[30] but her design made a great impression worldwide and was influential among foreign naval architects.

[28] France bought Dunderberg in 1867 to prevent Prussia from acquiring her,[28] and she served briefly in the French Navy as Rochambeau.