Instruct: Given a question, retrieve relevant passages that can help answer the question.
Query: When did trench warfare first start?
Trench warfare has become archetypically associated with the First World War of 1914–1918, when the Race to the Sea rapidly expanded trench use on the Western Front starting in September 1914.[15] By the end of October 1914 the whole front in Belgium and France had solidified into lines of trenches, which lasted until the last weeks of the war. Mass infantry assaults were futile in the face of artillery fire as well as rapid rifle and machine-gun fire. Both sides concentrated on breaking up enemy attacks and on protecting their own troops by digging deep into the ground.[16] Trench warfare also took place on other fronts, including in Italy and at Gallipoli.
At the start of the First World War, the standard infantry soldier's primary weapons were the rifle and bayonet; other weapons got less attention. Especially for the British, what hand grenades were issued tended to be few in numbers and less effective. This emphasis began to shift as soon as trench warfare began; militaries rushed improved grenades into mass production, including rifle grenades.
Behind the front system of trenches there were usually at least two more partially prepared trench systems, kilometres to the rear, ready to be occupied in the event of a retreat. The Germans often prepared multiple redundant trench systems; in 1916 their Somme front featured two complete trench systems, one kilometre apart, with a third partially completed system a further kilometre behind. This duplication made a decisive breakthrough virtually impossible. In the event that a section of the first trench system was captured, a "switch" trench would be dug to connect the second trench system to the still-held section of the first.
Temporary trenches were also built. When a major attack was planned, assembly trenches would be dug near the front trench. These were used to provide a sheltered place for the waves of attacking troops who would follow the first waves leaving from the front trench. "Saps" were temporary, unmanned, often dead-end utility trenches dug out into no-man's land. They fulfilled a variety of purposes, such as connecting the front trench to a listening post close to the enemy wire or providing an advance "jumping-off" line for a surprise attack. When one side's front line bulged towards the opposition, a salient was formed. The concave trench line facing the salient was called a "re-entrant." Large salients were perilous for their occupants because they could be assailed from three sides.
Trench warfare has been infrequent in recent wars. When two large armoured armies meet, the result has generally been mobile warfare of the type which developed in World War II. However, trench warfare reemerged in the latter stages of the Chinese Civil War (Huaihai Campaign), the Korean War (from July 1951 to its end), and at Dien Bien Phu and other later locations and engagements during the Vietnam War. During the Cold War, NATO forces routinely trained to fight through extensive works called "Soviet-style trench systems", named after the Warsaw Pact's complex systems of field fortifications, an extension of Soviet field entrenching practices for which they were famous in their Great Patriotic War (the Eastern Front of World War II).
A recent example of trench warfare is the War in Donbass. To consolidate and defend their territory, government and rebel forces have dug trenches and have initiated warfare reminiscent of World War I, with troops staying in and fighting from trenches for months at a time using cement mixers and excavators at their lines for digging network tunnels and deep bunkers for protection.[72] Since the Minsk peace agreements the front lines have not moved significantly and the two sides mostly fire mortars and sniper shots at each other. As a result both sides have dug elaborate networks of trenches and deep bunkers for protection.[73]
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 250m (270yd) of front-line trench system. Thereafter, the trench would require constant maintenance to prevent deterioration caused by weather or shelling.
The first methods of employing gas was by releasing it from a cylinder when the wind was favourable. This was prone to miscarry if the direction of the wind was misjudged. Also, the cylinders needed to be positioned in the front trenches where they were likely to be ruptured by enemy bombardment. Later, gas was delivered directly to enemy trenches by artillery or mortar shell, reducing friendly casualties significantly. Lingering agents could still affect friendly troops that advanced to enemy trenches following its use.
Mining saw a brief resurgence as a military tactic during the First World War, when army engineers attempted to break the stalemate of trench warfare by tunneling under no man's land and laying large quantities of explosives beneath the enemy's trenches. As in siege warfare, tunnel warfare was possible due to the static nature of the fighting. 
Trench warfare occurred when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage.[2] On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, camouflaged trapping pits, and other obstacles. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.
Trench warfare is a type of land warfare using occupied fighting lines consisting largely of military trenches, in which troops are well-protected from the enemy's small arms fire and are substantially sheltered from artillery. The most famous use of trench warfare is the Western Front in World War I. It has become a byword for stalemate, attrition, sieges, and futility in conflict.[1]
After the German withdrawal to the Hindenburg line in March 1917, no man's land stretched to over a kilometre in places. At the "Quinn's Post" in the cramped confines of the Anzac battlefield at Gallipoli, the opposing trenches were only 15 metres (16yd) apart and the soldiers in the trenches constantly threw hand grenades at each other. On the Eastern Front and in the Middle East, the areas to be covered were so vast, and the distances from the factories supplying shells, bullets, concrete and barbed wire so great, trench warfare in the West European style often did not occur.
By the end of First Battle of Ypres both sides started to dig in and trench warfare replaced the manoeuvre warfare that had featured during the Race to the Sea. The continuous trench lines of the Western Front now stretched from the North Sea to the Swiss frontier. The British Army held a small portion of this 400 mile front: from just north of the pre-war Belgium border to the River Somme in France, varying in length from in 1914, to over in 1918, in the area commonly known as Flanders.
The hand grenade came to be one of the primary infantry weapons of trench warfare. Both sides were quick to raise specialist grenadier groups. The grenade enabled a soldier to engage the enemy without exposing himself to fire, and it did not require precise accuracy to kill or maim. Another benefit was that if a soldier could get close enough to the trenches, enemies hiding in trenches could be attacked. The Germans and Turks were well equipped with grenades from the start of the war, but the British, who had ceased using grenadiers in the 1870s and did not anticipate a siege war, entered the conflict with virtually none, so soldiers had to improvise bombs with whatever was available (see Jam Tin Grenade). By late 1915, the British Mills bomb had entered wide circulation, and by the end of the war 75 million had been used.
Mainly as a result of the increasing firepower (such as machine guns) available to defensive forces, First World War trench warfare briefly revived a form of siege warfare. Although siege warfare had moved out from an urban setting because city walls had become ineffective against modern weapons, trench warfare was nonetheless able to use many of the techniques of siege warfare in its prosecution (sapping, mining, barrage and, of course, attrition), but on a much larger scale and on a greatly extended front.
The Crimean War (1853-1856) saw "massive trench works and trench warfare",[11] even though "the modernity of the trench war was not immediately apparent to the contemporaries".[12]
Trench warfare has become a powerful symbol of the futility of war.[17] Its image is of young men going "over the top" (over the parapet of the trench, to attack the enemy trench line) into a maelstrom of fire leading to near-certain death, typified by the first day of the Battle of the Somme (on which the British Army suffered nearly 60,000 casualties) or the grinding slaughter in the mud of Passchendaele.[18] To the French, the equivalent is the attrition of the Battle of Verdun in which the French Army suffered 380,000 casualties.[19]
With the development of armoured warfare, emphasis on trench warfare has declined but still occurs wherever battle-lines become static.
Only with the advent of accurate firearms did the use of trenches as positions for the defender of a fortification become common. Elaborate trench and bunker systems were employed by the Māori to withstand British artillery barrages and bayonet charges during the New Zealand Wars in the 1840s. Trench systems were also employed in the Russo-Japanese War[30] and American Civil War. The military usage evolved very quickly in the First World War, until whole systems of extensive main trenches, backup trenches (in case the first lines were overrun) and communication trenches had been developed, often stretching dozens of kilometres along a front without interruption, and some kilometres further back from the opponent's lines.
Though Napoleon Bonaparte started his military career in artillery, campaigning in the Napoleonic Wars generally emphasized movement rather than static entrenchment. But innovations in trench warfare became more prominent in the course of the 19th century.
The fundamental strategy of trench warfare in World War I was to defend one's own position strongly while trying to achieve a breakthrough into the enemy's rear. The effect was to end up in 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.
Some sectors of the front saw little activity throughout the war, making life in the trenches comparatively easy. When the I Anzac Corps first arrived in France in April 1916 after the evacuation of Gallipoli, they were sent to a relatively peaceful sector south of Armentières to "acclimatise". Other sectors were in a perpetual state of violent activity. On the Western Front, Ypres was invariably hellish, especially for the British in the exposed, overlooked salient. However, quiet sectors still amassed daily casualties through sniper fire, artillery, disease, and poison gas. In the first six months of 1916, before the launch of the Somme Offensive, the British did not engage in any significant battles on their sector of the Western Front and yet suffered 107,776 casualties. Only 1 in 2 men would return alive and unwounded from the trenches.
What became known as the submachine gun had its genesis in World War I, developed around the concepts of infiltration and fire and movement, specifically to clear trenches of enemy soldiers when engagements were unlikely to occur beyond a range of a few feet. The MP 18 was the first practical submachine gun used in combat. It was fielded in 1918 by the German Army as the primary weapon of the stormtroopers, assault groups that specialised in trench combat.
At the start of the war there were no trench maps--trench warfare did not develop until late 1914, and the British army did not possess in the Summer of 1914 the logistical and technical support that making trench maps would have required. The British Army went to war with maps more suited to a "war of movement", i.e. small scale maps, of a scale just about adequate for marching. Once the line had become static after the Battle of the Aisne and the Race for the Sea, the need for accurate, detailed maps of the new trench networks became urgent.
Landmines were widely used in WWI trench and tunnel warfare to destroy or disrupt enemy's trench lines.[50][51]