Dennis Hart Mahan was a noted American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 military theorist

Military theory

Military theory is the analysis of normative behavior and trends in military affairs and military history, beyond simply describing events in war and military theories, especially since the influence of Clausewitz in the nineteenth century attempt to encapsulate the complex cultural, political and...

 and professor at the United States Military Academy

United States Military Academy

The United States Military Academy at West Point is a four-year coeducational federal service academy located at West Point, New York. The academy sits on scenic high ground overlooking the Hudson River, north of New York City...

 at West Point

West Point, New York

West Point is a federal military reservation established by President of the United States Thomas Jefferson in 1802. It is a census-designated place located in Town of Highlands in Orange County, New York, United States. The population was 7,138 at the 2000 census...

 from 1824-1871. He was the father of American naval historian and theorist Rear Admiral Alfred Thayer Mahan

Alfred Thayer Mahan

Alfred Thayer Mahan was a United States Navy flag officer, geostrategist, and historian, who has been called "the most important American strategist of the nineteenth century." His concept of "sea power" was based on the idea that countries with greater naval power will have greater worldwide...

. Of his other four children, his son Frederick August Mahan also graduated from West Point in 1867.

Biography

Dennis Hart Mahan was the child of Irish-Catholic immigrants. He was baptized at New York City

New York City

New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

, though like other immigrant children of that era, e.g., General Philip Sheridan

Philip Sheridan

Philip Henry Sheridan was a career United States Army officer and a Union general in the American Civil War. His career was noted for his rapid rise to major general and his close association with Lt. Gen. Ulysses S...

, it is unclear whether Mahan was born at New York or in Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

. Mahan graduated from West Point in 1824, first in his class. Such was his acumen that in his third year he was appointed acting assistant professor of mathematics. After graduation, he started teaching at the Military Academy with the very next class of cadets (1824). In 1826, he was sent to Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 to study advanced engineering techniques and military institutions. Upon returning to West Point in 1830, he was promoted to Professor of Civil and Military Engineering. He resigned his commission in 1832 to accept the position of Chair of the Engineering Department.

An important influence on the military conduct of the American Civil War

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

 and Civil Engineering, Mahan is best understood as an educator and technology transfer agent, not a theorist. Mahan almost singlehandedly compiled and transferred the best of European engineering to the United States and other English-speaking parts of the world. Virtually all 19th century American engineering schools were started with West Point-educated faculty or adopted its texts.

As a professor of military science at West Point, in addition to engineering methodology, Mahan promoted the development of professionalism and wrote extensively on fixed fortifications, field fortifications, strategy and tactics. His books on military thought were widely influential. His writings became standard textbooks in the worldwide field from the time they were written until after World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. Mahan also founded the Napoleon Seminar at West Point, where advanced under-graduates and senior officers including Lee

Robert E. Lee

Robert Edward Lee was a career military officer who is best known for having commanded the Confederate Army of Northern Virginia in the American Civil War....

, Reynolds

John F. Reynolds

John Fulton Reynolds was a career United States Army officer and a general in the American Civil War. One of the Union Army's most respected senior commanders, he played a key role in committing the Army of the Potomac to the Battle of Gettysburg and was killed at the start of the battle.-Early...

, Thomas

Edward Lloyd Thomas

Edward Lloyd Thomas was a Confederate infantry general during the American Civil War from the state of Georgia. He was an uncle to famed American Old West lawman Heck Thomas who helped bring down the Doolin Dalton Gang....

 and McClellan

George B. McClellan

George Brinton McClellan was a major general during the American Civil War. He organized the famous Army of the Potomac and served briefly as the general-in-chief of the Union Army. Early in the war, McClellan played an important role in raising a well-trained and organized army for the Union...

, studied and discussed the great European wars, Napoleon and Frederick the Great.

Professor Mahan's lectures and writings about military fortifications and strategy were instrumental in the conduct of the Civil War by the officers on both sides. Most of the Civil War commanders, whether Union

Union Army

The Union Army was the land force that fought for the Union during the American Civil War. It was also known as the Federal Army, the U.S. Army, the Northern Army and the National Army...

 or Confederate, learned about entrenchment

Entrenchment

Entrenchment or Entrenched may refer to:* Military trenches with relation to Trench warfare, especially that of World War I *Entrenchment as a feature of a Constitution, making it more difficult to amend* Entrenched clause within a constitution...

, fortification

Fortification

Fortifications are military constructions and buildings designed for defence in warfare and military bases. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs...

s, and how to conduct warfare in the classes that he taught at West Point, and from his pre-Civil War writings.

While the influence of Mahan and West Point on the Civil War remains controversial and neglected, it is not difficult to find many of the Civil War's tactics and strategies presaged in Mahan's work. Topography and the use of terrain to advantage became important thanks to Mahan, as well as the principles of concentration, "celerity" and calculated risk. Lee used the Blue Ridge Mountains

Blue Ridge Mountains

The Blue Ridge Mountains are a physiographic province of the larger Appalachian Mountains range. This province consists of northern and southern physiographic regions, which divide near the Roanoke River gap. The mountain range is located in the eastern United States, starting at its southern-most...

 to screen his invasions of Pennsylvania

Pennsylvania

The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

 and Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

. Grant

Ulysses S. Grant

Ulysses S. Grant was the 18th President of the United States as well as military commander during the Civil War and post-war Reconstruction periods. Under Grant's command, the Union Army defeated the Confederate military and ended the Confederate States of America...

 used rivers to screen his approaches to Vicksburg and Richmond

History of Richmond, Virginia

The history of Richmond, Virginia, as a modern city, dates to the early 17th century, and is crucial to the development of the colony of Virginia, the United States Revolutionary War, and the Civil War...

. The French called this envelopment strategy "la manoeuvre sur les derrières." At Vicksburg, after the envelopment, Grant used a strategy of the central position to defeat his opponent in detail, a Napoleon tactic well-known to Mahan's admirer and Grant's lieutenant WT Sherman, if not Grant himself. At Gettysburg

Battle of Gettysburg

The Battle of Gettysburg , was fought July 1–3, 1863, in and around the town of Gettysburg, Pennsylvania. The battle with the largest number of casualties in the American Civil War, it is often described as the war's turning point. Union Maj. Gen. George Gordon Meade's Army of the Potomac...

, Reynolds saw the opportunity for a Corps d'Armee engagement where his leading Corps held off Confederate attacks while the mass of the Union army concentrated. The Union's disposition on Cemetery Ridge at Gettysburg is almost perfectly sited according to Mahan's recommendations in "Field Fortifications" for disrupting an opponent's artillery fire. Meade's inability to trap Lee after Gettysburg certainly had something to do with Lee heeding Mahan's advice on planning for a protected line of retreat. Perhaps the Union and Confederate armies would have adopted flexible and resilient division and corps formations in any event, but some credit for the adoption of these extremely important military formations belongs to West Point and Mahan and their contribution to the professional development of most of the Civil War's important officers.

Mahan Hall at the United States Military Academy

United States Military Academy

The United States Military Academy at West Point is a four-year coeducational federal service academy located at West Point, New York. The academy sits on scenic high ground overlooking the Hudson River, north of New York City...

 at West Point was named in his honor. Built in 1971, it houses the Academy's Departments of Civil & Mechanical Engineering (CME) and Systems Engineering. Mahan Hall at the U.S. Naval Academy and the Naval War College

Naval War College

The Naval War College is an education and research institution of the United States Navy that specializes in developing ideas for naval warfare and passing them along to officers of the Navy. The college is located on the grounds of Naval Station Newport in Newport, Rhode Island...

 were named for his son, Alfred Thayer Mahan

Alfred Thayer Mahan

Alfred Thayer Mahan was a United States Navy flag officer, geostrategist, and historian, who has been called "the most important American strategist of the nineteenth century." His concept of "sea power" was based on the idea that countries with greater naval power will have greater worldwide...

.

Books by Dennis Hart Mahan

• Treatise on Field Fortifications (1836)
• Elementary Course of Civil Engineering (1837; revised 1868)
• Elementary Treatise on Advanced Guard, Outposts, and Detachment Service of Troops (1847; revised, 1862)
• Summary on the Cause of Permanent Fortifications and of the Attack and Defense of Permanent Works (1850)
• Elementary Treatise on Industrial Drawing (1853)
• Editor, with additions, the American edition of Mosely's Mechanical Principles of Engineering and Architecture (1856)
• Descriptive Geometry, as applied to the Drawing of Fortifications and Stereometry (1864)
• An Elementary Course on Military Engineering [covering] Field Fortifications, Military Mining, and Siege Operations (1865)
• Permanent Fortifications (1867)