Horace Holden Thayer, Jr. (1878-1959) was a naval architect, mechinical engineer, and businessman. Thayer was born on 11 March 1878 in Yonkers, New York to Horace Holden Thayer (1847-1924) and Frances Ella Barry Thayer (1855-1931). He attended Cornell University, graduating in 1900 with a degree in Mechanical Engineering. Following graduation he was employed by three shipyards in the drafting room and eventually as a naval architect.

Thayer married Anna Pim Savery Thayer (1876-1960) in 1904. She was the daughter of Thomas H. Savery (1837-1910) and Sarah Pim Savery (1837-1928). Thomas H. Savery was president of Pusey, Jones and Company, a major shipbuilding company in the late nineteenth and early twentieth centuries. The couple had one daughter and made their home in Haverford, Pennsylvania

In 1907 Thayer went into business as a naval architect and marine surveyor. Between 1909 and 1914 Thayer worked for the Delaware Construction Company which was a building company, constructing residential houses in downtown Wilmington, Delaware. Thayer was company treasurer from the company's founding in 1909. The Delaware Construction Co. was a subsidary of the National Real Estate Trust Company, which provided loans and financing for the properties.

In 1917 he joined the United States Shipping Board Emergency Fleet Corporation as an assistant to the Naval Architect and eventually as head of the Technical Department. Subsequent to his service there, Thayer was a naval architect and ship surveyor in Delaware and Pensylvania. Thayer died on 18 February 1959 in Pennsylvania.