Strategy

The fundamental strategy of trench warfare was attrition; the process of progressively grinding down the opposition's resources until, ultimately, they are no longer able to wage war. This did not prevent the ambitious commander from pursuing the strategy of annihilation—the ideal of an offensive battle which produces victory in one decisive engagement. The British commander, General Douglas Haig, was constantly seeking a "breakthrough" which he could exploit with his cavalry divisions. His major trench offensives—the Somme in 1916 and Flanders in 1917—were conceived as breakthrough battles but both degenerated into costly attrition. The Germans actively pursued a strategy of attrition in the Battle of Verdun, the sole purpose of which was to "bleed the French Army white".

Tactics

The popular image of a trench warfare infantry assault is of a wave of soldiers, bayonets fixed, going "over the top" and marching in a line across no man's land into a hail of enemy fire. This indeed was the standard method early in the war and successful examples are few. The more common tactic was to attack at night from an advanced post in no man's land, having cut the barbed wire entanglements beforehand.

In 1917, the Germans innovated with the "infiltration" tactic where small groups of highly trained and well equipped troops would attack vulnerable points and bypass strong points, driving deep into the rear areas. The distance they could advance was still limited by their ability to supply and communicate.

The role of artillery in an infantry attack was twofold; firstly in preparation by killing or driving off the enemy garrison and destroying his defences, and secondly in protecting the attacking infantry by providing an impenetrable "barrage" or curtain of shells to prevent an enemy counter-attack. The first attempt at sophistication was the "lifting barrage" where the first objective of an attack was intensely bombarded for a period before the entire barrage "lifted" to fall on a second objective further back. However, this usually expected too much of the infantry and the usual outcome was that the barrage would outpace the attackers, leaving them without protection. This resulted in the use of the "creeping barrage" which would lift more frequently but in smaller steps, sweeping the ground ahead and moving so slowly that the attackers could usually follow closely behind it.

Capturing the objective was half the successful battle—the battle was only won if the objective was held. The attacking force would have to advance with not only the weapons required to capture a trench but also the tools—sandbags, picks & shovels, barbed wire— to fortify and defend from counter-attack. The Germans placed great emphasis on immediately counter-attacking to regain lost ground. This strategy cost them dearly in 1917 when the British started to limit their advances so as to be able to meet the anticipated counter-attack from a position of strength.

Communications

The main difficulty faced by an attacking force in a trench battle was reliable communications. Wireless communications were still in their infancy so the available methods were telephone, semaphore, signal lamps, carrier pigeons and runners, none of which were particularly reliable. Telephone was the most effective but the lines were extremely vulnerable to shell fire so would usually be cut early in a battle. In an attempt to counter this, telephone lines would be laid in a ladder pattern to provide multiple redundant paths. Flares and rockets were used to signal an objective was reached or to call for pre-arranged artillery support.

It was not unusual for a battalion or brigade commander to wait 2 or 3 hours for word on the progress of an attack, by which time any decision made based on the message would probably be long out of date. A similar period would pass when transferring the news to the division, corps and army headquarters. Consequently the outcome of many trench battles were decided by the company and platoon commanders in the thick of the fighting.