How did the trenches come about in ww1? | AskHistorians Archive Observer

Part 1

I’ve answered variations of this question in the past (helpfully linked by u/Sjoerde), but I’ll tackle it more directly here so we can refer to it again in the future.

I studied the British army’s use of entrenchments during the transitional phrase from mobile to trench warfare on the Western Front in 1914, so most of my examples come from that research. Although the details might differ between armies, we see parallel developments in the French and German cases as well. Thus, the British experience is in many ways indicative of the overall process.

I’m going to start off by giving some background about the tactical use of entrenchment and how armies planned to use trenches and field fortifications in war. Then I’ll look at how trenches first appeared on the Western Front. Finally, briefly, I’ll look at how it was possible for trench systems to be improved.

Background

All armies on the Western Front went to war in 1914 prepared to use entrenchments. Late nineteenth- and early twentieth-century Improvements in firepower, mostly in the form of quick-firing artillery and machine guns, made the modern battlefield exceedingly deadly. Thus, cover (that is, trenches) became invaluable. We see trenches and other similar types of fieldworks being used in the American Civil War, the Russo-Ottoman War, the Boer War in South Africa, and the Russo-Japanese War.

The British, for example, learned firsthand the importance of trenches in the Boer War (1899-1902). The British army went into that war using trenches only a few feet deep. By the end of the fighting, however, tactical manuals advocated digging trenches at least four or five feet deep while augmenting trench systems with cover trenches, communications trenches, and barbed wire.

Tactically, trenches served two primary purposes: (1) to shelter troops from enemy fire and (2) to bolster a position’s ability to defend against infantry attack. When trenches started appearing in 1914, armies envisioned them as means to an end: if a position was strengthened with trenches, then fewer men would be needed to defend the front line; those men could then be allocated to a general reserve earmarked for a counterattack.

Thus—and this is crucially important—no side envisioned the deadlock that we get by December 1914. Trenches and field fortifications were conceived of as being temporary defenses meant to strengthen an army’s ability to deliver a knockout counterattack.

The First Trenches, 1914

The WWI battlefield was deadlier than ever, and trenches appeared almost immediately. I don't have the space to go into the details, but I’ve written an extensive answer about the nature of “open” warfare in 1914 here:

What was "open" combat like in WW1? Specifically larger battles like the Battles of the Frontiers and when the Germans broke through the lines during the Kaiserschlacht offensives.

I recommend reading that answer before continuing so you have the necessary context about why trenches were so vital.

Entrenchment in 1914 took one of two forms: (1) preemptive entrenchment and (2) reactionary entrenchment.

Let’s look at preemptive entrenchment first.

Preemptive entrenchment was when an army preemptively constructed field defenses in anticipation of defending a position. Off the top of my head, I can think of two good examples of this. First, in early September 1914, as the French and British were falling back toward Paris, the French constructed trenches and fortifications on the Grand Couronee near Nancy. Second, after the Germans retreated from the Marne river in mid-September, First and Second armies withdrew behind the River Aisne and dug in on the northern heights of the river valley.

Let’s take a look at the second instance in more detail.

The Battle of the Marne, in short, was a strategically decisive engagement in September 1914 where the French and British forced the Germans to withdrawal in order to avoid being outflanked. Subsequently, Moltke, the chief of the German General Staff, ordered his First and Second Armies to take up a position on the northern side of the River Aisne. The intent was the hold the position while giving his forces time to regroup and prepare for another move against Paris. The Aisne position was highly defensible and controlled the high ground overlooking the river valley below. The Germans sent their engineers ahead of the army to begin work on the defenses, and by the time German troops arrived at the position on 12-13 September, the positions were nearly finished.

The British Expeditionary Force (BEF) and French Fifth and Sixth Armies attacked the position on 14 September. The attack failed to dislodge the Germans from their heights, leading to our second type of entrenchment: reactionary entrenchment.

In reactionary entrenchment, a force has attacked or made contact with the enemy, then digs in to secure the captured ground.

Let’s look at the British attack on the German positions north of the Aisne on 14 September as an example.

The bulk of the British army crossed the river and began advancing up the slopes toward the German positions, but the Germans were dug in and supported by heavy artillery. To make matters worse, the weather was rainy and foggy, so communications were difficult. The attack was chaotic, and the British didn’t make much headway. However, units didn’t retreat and withdraw back behind the river. Rather, they dug in to secure their positions on the northern bank.

Now, when units physically dug trenches, they avoided coming under enemy fire in two ways. First, digging parties were sent back to prepare positions while screening forces maintained contact with the enemy. In this way, the screening parties kept the Germans busy while the digging parties entrenched. When the positions were sufficiently deep, the screening parties would withdraw and occupy the trenches. Second, the British entrenched on reverse slopes. That is, they dug in behind the crest of hills so German artillery didn’t have a direct line of sight to their trench lines. The British positions were therefore shielded from direct artillery fire and quite safe. Entrenching on reverse slopes became standard practice in the British army until 1916.

We see reactionary entrenchment all along the line from the Aisne to Flanders in October 1914. When British and German armies collided in Flanders, for example, British units would attack, make contact with the enemy, fail to make much headway, and dig in to hold their ground. They’d then try to attack again the next day, at which point they’d either dig a new line or go back to their original trenches.

For more information about digging trenches, specifically how long it took, check out my answer to the following question:

“In ww1 how long did it take to make a trench, and how did certain trenches have bunkers and stone in them?”

So armies dug in either preemptively with the expectation of being attacked or dug in to hold ground captured during an attack. In the former case, engineers constructed defenses away from the heat of the battle. In the latter case, digging parties were covered by screening forces or, if possible, trenches were positioned on reverse slopes so they were difficult to hit with direct artillery fire.

Continued in Part 2 below.