He is best known for his civil engineering efforts, such as the creation of the Tidal Basin in Washington, D.C., and for laying out the Panama Canal.

Among his classmates were Medal of Honor recipient First Lieutenant Alonzo Cushing, and Major Generals George Custer, USA, and Pierce Manning Butler Young, CSA.

[2] During the Siege of Vicksburg, Hains was cited for meritorious conduct while serving as the interim chief engineer of the XIII Corps.

He was the chief engineer for the construction of Morris Island light, at the entrance of the harbor at Charleston, South Carolina, from 1872 to 1876.

The crime, and the subsequent separate trials for the brothers, became one of the notorious cases of its day, front-page news across the country.

In recognition of his long and distinguished career, Hains was promoted to major general on the retired list in 1916.

[4] Hains was the oldest officer to serve on active duty since Major General John E. Wool retired in 1863 at the age of 79.

His grandson and namesake, Peter C. Hains III, was also a major general in the U.S. Army and competed in the 1928 Summer Olympics.