Henry Larcom Abbot was born in Beverly, Massachusetts. Abbot attended West Point and graduated second in his class (which included Jeb Stuart and G. W. Custis Lee) with a degree in military engineering in 1854. Initially he had wanted to join the Artillery, but shortly after graduation, a classmate convinced him to choose the Engineers. He was commissioned as a brevet second lieutenant in the U.S. Army on July 1, 1854, second lieutenant on October 2, 1855 and first lieutenant on July 1, 1857.  In 1855, Abbot was assigned to work with Lieutenant Robert Williamson’s Pacific Railroad Survey in California and Oregon. To honor his work on this survey, the California Geological Survey named Mount Abbot in the Sierra Nevada after him in 1873.

While serving in the Army, Lieutenant Abbot and Captain Andrew Humphreys conducted several scientific studies of the Mississippi River. They most notably studied the Mississippi river’s flow starting at the Ohio River and going southward down to its base level at the Gulf of Mexico. They attempted to use several European formulas for stream discharge they had learned at West Point, but came to discover that they were all flawed. They then developed their own formula which ultimately also proved to be faulty, most notably they forgot to account for the roughness of slopes in river canals. Although the formula was not without flaw it influenced the evolution of hydrology and was instrumental in the establishing of an United States Army Engineer School at Fort Totten in New York City.

At the outbreak of the Civil War, Lt. Abbot was assigned to Brigadier General Irvin McDowell’s forces and was wounded at the First Battle of Bull Run. He later became a Topographical Engineer in the Army of the Potomac during the Peninsula Campaign and aide-de-camp to Brig. Gen. Andrew Humphreys. During this campaign he was brevetted major for his service at the siege of Yorktown. On July 18, 1862, Abbot was promoted to captain in the Regular Army and was assigned to the staff of Brig. Gen. John G. Barnard until November 11, 1862. He was then briefly assigned as a Topographical Engineer in the Department of the Gulf. On January 19, 1863 he was appointed colonel of the 1st Connecticut Heavy Artillery but on March 3, 1863 was transferred to the Washington Defenses where he commanded a brigade.

In May 1864 he was transferred to command the Artillery during the siege of Petersburg. On December 12, 1864, President Abraham Lincoln nominated Abbot for appointment to the grade of brevet brigadier general of volunteers to rank from August 1, 1864 and the U.S. Senate confirmed the appointment on February 20, 1865. In December 1864 he was placed in command of all siege artillery in the Army of the Potomac and Army of the James that were besieging Petersburg. In January 1865 General Alfred H. Terry requested General Abbot accompany his expeditionary force to Fort Fisher. Abbot commanded a provisional brigade of siege artillery during the successful Second Battle of Fort Fisher.

Abbot was mustered out of the volunteer service on September 25, 1865. On January 13, 1866, President Andrew Johnson nominated Abbot for appointment to the grade of brevet major general of volunteers to rank from March 13, 1865 and the U.S. Senate confirmed the appointment on March 12, 1865. On July 17, 1866, President Johnson nominated Abbot for appointment to the grade of brevet brigadier general in the regular army to rank from March 13, 1865 and the U.S. Senate confirmed the appointment on July 23, 1865.

In the post-war years, Abbot continued to serve in the U.S. Army Engineers. He was promoted to major on November 11, 1865. He was assigned to the command of the engineer battalion at Willet’s Point, New York. He created the army’s Engineer School of Application there, and served on numerous boards, including the Board on the Use of Iron in Permanent Defenses, the Board of Engineers for Fortifications, the Gun Foundry Board, the Board on Fortifications and Other Defenses, and the Board of Ordnance and Fortifications. Abbot’s influence can be seen in many facets of the coast defense systems of the United States of that period—in particular, in the submarine mine system, and in the use of seacoast mortars. Abbot advocated the massing of 16 mortars in 4 sets of 4, which would fire simultaneously at the enemy warships. The plan became known as the “Abbot Quad”.

After his retirement from the army, Abbot continued to work as a civil engineer and was employed as a consultant for the locks on the Panama Canal.  “Brig. Gen. Henry Larcom Abbot, coauthor of a classic work on the hydrology of the Mississippi River, began his involvement with the Panama Canal as a member of the new French canal company’s Comité Technique and Comité Statutaire, from 1897 to 1900. While the United States was assuming responsibility for building the Canal, Abbot worked for the French company as a consulting engineer during the transitional period, dividing his time between Paris and the isthmus. After the Americans assumed control of the project Abbot served from 1905 to 1906 on the Board of Consulting Engineers, a body appointed by Theodore Roosevelt and charged with the preparation of a plan for canal construction. The majority of the board recommended a sea-level canal. The minority report, probably written largely by Abbot, helped to persuade Roosevelt and Secretary of War William Howard Taft to adopt a plan for a lock canal. Abbot’s last service to the canal was as a member of the Panama Canal Slide Committee in 1915.”

“Abbot’s numerous articles and one book account for over half of the entries in this bibliography. They range widely over several topics. In addition to arguing for a lock canal he insisted that the Americans abandon once and for all any thought of building a canal in Nicaragua. Other articles answered critics who asserted that Panama was too hot, wet, and unhealthy, and that the area was subject to earthquakes. Abbot successfully presented the case for creating two artificial lakes instead of one. He maintained that the wild and unpredictable Chagres could be tamed and made useful in the building and operation of the canal.”

Abbot retired as a colonel on August 13, 1895. On April 23, 1904, he was appointed Brigadier General, U.S.A., retired.  Henry Larcom Abbot died on October 1, 1927 at Cambridge, Massachusetts. He is buried at Mount Auburn Cemetery, Cambridge.