Trench warfare
Construction

Trenches were longer, deeper, and better defended by steel, concrete, and barbed wire than ever before. They were far stronger and more effective than chains of forts, for they formed a continuous network, sometimes with four or five parallel lines linked by interfacings. They were dug far below the surface of the earth out of reach of the heaviest artillery....Grand battles with the old maneuvers were out of the question. Only by bombardment, sapping, and assault could the enemy be shaken, and such operations had to be conducted on an immense scale to produce appreciable results. Indeed, it is questionable whether the German lines in France could ever have been broken if the Germans had not wasted their resources in unsuccessful assaults, and the blockade by sea had not gradually cut off their supplies. In such warfare no single general could strike a blow that would make him immortal; the "glory of fighting" sank down into the dirt and mire of trenches and dugouts.

Early World War I trenches were simple. They lacked traverses, and according to pre-war doctrine were to be packed with men fighting shoulder to shoulder. This doctrine led to heavy casualties from artillery fire. This vulnerability, and the length of the front to be defended, soon led to frontline trenches being held by fewer men. The defenders augmented the trenches themselves with barbed wire strung in front to impede movement; wiring parties went out every night to repair and improve these forward defences.

The small, improvised trenches of the first few months grew deeper and more complex, gradually becoming vast areas of interlocking defensive works. They resisted both artillery bombardment and mass infantry assault. Shell-proof dugouts became a high priority.

A well-developed trench had to be at least 2.5 m (8 ft) deep to allow men to walk upright and still be protected.

There were three standard ways to dig a trench: entrenching, sapping, and tunneling. Entrenching, where a man would stand on the surface and dig downwards, was most efficient, as it allowed a large digging party to dig the full length of the trench simultaneously. However, entrenching left the diggers exposed above ground and hence could only be carried out when free of observation, such as in a rear area or at night. Sapping involved extending the trench by digging away at the end face. The diggers were not exposed, but only one or two men could work on the trench at a time. Tunnelling was like sapping except that a "roof" of soil was left in place while the trench line was established and then removed when the trench was ready to be occupied. The guidelines for British trench construction stated that it would take 450 men 6 hours at night to complete 250 m (270 yd) of front-line trench system. Thereafter, the trench would require constant maintenance to prevent deterioration caused by weather or shelling.

Trenchmen were a specialized unit of trench excavators and repairmen. They usually dug or repaired in groups of four with an escort of two armed soldiers. Trenchmen were armed with one 1911 semi-automatic pistol, and were only utilized when either a new trench needed to be dug or expanded quickly, or when a trench was destroyed by artillery fire. Trenchmen were trained to dig with incredible speed; in a dig of three to six hours they could accomplish what would take a normal group of frontline infantry soldiers around two days. Trenchmen were usually looked down upon by fellow soldiers because they did not fight. They were usually called cowards because if they were attacked while digging, they would abandon the post and flee to safety. They were instructed to do this though because through the war there were only around 1,100 trained trenchmen. They were highly valued only by officers higher on the chain of command.
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