An American observer of that war, George B. McClellan, noted the improved power of the entrenched defense, while the outstanding American military theorist of the time, Dennis Hart Mahan, advocated before the Civil War an entrenched but active defense, and expressed doubts about the frontal assault of fortified positions. Mahan and his supporters represented one school of thought, and their concerns were reinforced by the introduction of the rifled musket in the mid‐1850s. However, an opposite and more popular school of thought emphasized offensive Napoleonic warfare. This approach also benefitted from successful American assaults in the Mexican War (1846–48).
Thus, in the first two years of the Civil War, entrenchments were often ignored. However, from 1863 on, as the rifled musket made an even greater impact, as infantry dominated the battlefield, as the cost of offensive warfare in casualties climbed steeply, and as the Confederate army went more frequently onto the defensive, entrenchments became much more significant. These often consisted of breastworks of logs, since engineers and digging tools were in short supply. But where possible, those who believed in the value of trenches used them, although others deprecated their use, believing that they lowered troop morale. Still others, like Gen. Ulysses S. Grant, were inconsistent in their attitude toward entrenchments.
This move toward trench warfare can be seen in sieges such as at Vicksburg (1863) and Petersburg (1864). At the Siege of Vicksburg, for example, General Grant penned in a Confederate army, which constructed strongpoints and forts every few hundred yards for the artillery, and linked these strongpoints with rifle pits and trenches. Grant tried two attacks upon these defenses, and both failed, with heavy loss of life. Grant then turned to Vauban‐style besieging tactics and began sapping and mining toward the defensive works. So close did the trench lines approach each other that the night pickets were able to fraternize. But with daylight it was “Watch out, Johnnie, and hunt your hole.” Eventually, Grant wore down the defenders. Similarly, at the Siege of Petersburg, the lengthy siege with trenchworks and mining failed to take the city, which only surrendered through lack of supplies and attrition.
Vicksburg and Petersburg showed the power of defensive entrenchments during sieges when protected by artillery and rifles. Equally, in the last three years of the Civil War, both offensive and defensive entrenchments revealed their value in battle, for example, at Cold Harbor (1864), and at Kennesaw Mountain (1864). Dennis Mahan's school of thought had been vindicated by the Civil War. However, other armies did not appreciate the change in warfare, as the shadow of Napoleon continued to emphasize offensive ideas. Thus, the Franco‐Prussian War, the Boer War in South Africa, and the Russo‐Japanese War all demonstrated the problems of taking entrenchments that were defended by improved rifles, long‐range artillery, and increasingly, machine guns.
Trench warfare of World War I continued the nineteenth‐ and early twentieth‐century trend toward increased power of the entrenched defense. Weapons were now even more powerful, and these forced the infantry underground into long lines of trenches, which spread across the entire western front by late 1914. The United States entered the war in April 1917, under the command of Gen. John J. Pershing, who hindered his troops' efficiency by advocating “open warfare.” Pershing believed the French and British had bogged down in defeatist trench warfare, and that the American Expeditionary Forces (AEF) could break through enemy trenches and achieve open warfare by the use of initiative, the rifle, and the bayonet. Pershing stated that victory “could not be won by the costly process of attrition, but it must be won by driving the enemy out into the open and engaging him in a war of movement.” However, Pershing ignored the power of trench defenses, and so AEF troops frequently suffered heavy losses, such as the attack in June 1918 at the Battle of Belleau Wood, where the U.S. Second Division took nearly 9,000 casualties.
Nevertheless, Pershing felt vindicated by the AEF success at the Battle of St. Mihiel in September 1918, where rapid advances did overrun trenches and barbed wire. Next, the AEF took part in the Meuse‐Argonne Offensive. This ran into logistical problems, but inexperience also led to underuse of hand grenades and gas masks, while frontal attacks against German trenches and positions created severe losses among the Americans. In fact, the AEF was actually waging costly attrition warfare, despite Pershing's ideas. Late in October 1918, the AEF reorganized and assimilated trench warfare lessons. Assault teams were created to deal with German machine guns, while the main offensive bypassed these strongpoints. This tactic, plus the use of other weapons, produced a combined arms approach to dealing with German defenses. In the early morning of 1 November 1918, the AEF's First Army attacked in this fashion and broke through all German defenses. Pershing's wish was finally achieved: open warfare had arrived.
Trench warfare, defined as combat with both sides in trenches, apparently came to an end with the armistice in 1918. However, dug‐in positions remained a feature of warfare, as the later twentieth century showed. During World War II, in Normandy after the D‐Day landing, the defenses of the bocage (hedgerow) countryside slowed down Allied forces until an American sergeant devised steel teeth mounted on a Sherman tank to cut through the roots of the thick hedges. In the Pacific War, Japanese soldiers on Iwo Jima and Okinawa had to be driven out of their entrenchments and caves with artillery, tanks, rockets, flame throwers, and dynamite. Then, in the Korean War, especially between November 1951 and July 1953, both sides dug in and resumed a static World War I form of trench warfare on hilltops and mountain ridges, complete with “no‐man's‐land.” During the Vietnam War, U.S. forces occasionally came across remarkable series of enemy trenches and underground systems, such as the tunnels at Cu Chi. Finally, in the Persian Gulf War, the Iraqi Army dug in with extensive defenses of sand berms, trenches, foxholes, and minefields. Led by American divisions, United Nations forces used bulldozers and antimine tank plows to cut lanes through the defenses, as well as plowing under trenches that contained infantry resisters.
Recent conflicts show that trench warfare still continues. Yet the basic contradiction of this style of fighting remains—trench warfare is essentially defensive, but armies continually seek offensive success.
[See also Engineering, Military; Iwo Jima, Battle of; Okinawa, Battle of; World War I: Military and Diplomatic Course; World War II: Military and Diplomatic Course; World War II, U.S. Naval Operations in: The Pacific.]
Tom Mangold and and John Penycate , The Tunnels of Cu Chi, 1985.
Bill Ross , Iwo Jima: Legacy of Valour, Vanguard, New York, 1985.
Paul Braim , The Test of Battle: The American Expeditionary Forces in the Meuse‐Argonne Campaign, 1987.
Tim Travers , The Killing Ground: The British Army, the Western Front, and the Emergence of Modern Warfare, 1900–1918, 1987.
Edward Hagerman , The American Civil War and the Origins of Modern Warfare, 1988.
David Trask , The AEF and Coalition Warmaking, 1917–1918, 1993.