Trench Stroming in World War One:
Trench storming was obviously important, since it was the only possible way to break through the unflankable 400-mile Western Front. What’s more interesting is to see whether it actually worked. According to popular belief this is a no-brainer–assaults during World War One never worked! They were just a complete waste of human life by unimaginative and out-of-touch generals living in mansions miles behind the front line who had no understanding of the number of lives they were throwing away to no purpose! This stereotype is quite simply wrong. Trench assaults could and often did succeed.
Until the end of 1914 the war was obviously extremely mobile, yet even after it settled down into a war of attrition, it was still possible to break the deadlock. At Neuve Chapelle in March 1915, the British broke through the single German trench line, thanks to a rapid (35-minute) and extremely concentrated bombardment. This success wasn’t followed through quickly enough to achieve an operational breakthrough, but tactically, the British had well and truly succeeded in overcoming the German defences. The British took the wrong lesson from this; they reasoned that longer and heavier barrages would allow even greater successes, failing to realize that the barrage worked so well at Neuve Chapelle only because it was short and focused on a narrow section of the front. At Loos in September-October 1915, the dispersed bombardment failed to destroy the German defences, although even then, the British were able to break through the defences; again, breakthrough was only prevented by the late arrival of reserves. By the time the offensive could renew, the Germans had reconstituted their defence; but again, the attack was a tactical success.
After Neuve Chapelle, the Germans took the correct lesson, realizing that one trench line was not enough; thereafter they developed a defence in depth, with at least three lines of trenches to absorb the momentum of attacks. This was the situation at the Somme, the classic futile assault. Yet the assault was in numerous places successful; in fact, the British 30th Division was able to break right through the depth of the German defences, within sight of the green fields beyond. That this breach was not exploited does not discount the fact that a trench assault had succeeded in defeating three successive lines of German defences. This map (http://en.m.wikipedia.org/wiki/File:Battle_of_the_Somme_1916_map.png) shows the ground captured from July-November 1916; although such gains weren’t enough to change the strategic situation, and despite the fact that casualties (on both sides) were extreme, it just can’t be argued that assaults were always unsuccessful.
At the start of 1917, the Germans withdrew part of their line to prepared positions at the Hindenburg (or Siegfried) line. The German defensive art was reaching its most advanced; soldiers manned three successive lines of well-built trenches, with deep shelters to protect them from the barrage and well-practised defensive artillery. Yet these defences continued to be taken, largely because Allied offensive developments–air reconnaissance, creeping barrages, and the tank–kept pace with German defensive developments. The Battle of Arras from April-May saw tactical success, notably the capture of Vimy Ridge by the Canadians. Probably the most decisive success of the war, at Messines, took place in June; the ridge was taken with ease after a series of 19 huge mines demolished the German trenches (it’s debatable whether this counts as a trench storming, since the trenches were virtually gone by the time the assault began). The subsequent Third Battle of Ypres was wasteful of manpower and achieved no strategic aim, but the village of Passchendaele was captured nonetheless. The Battle of Cambrai in November was an undeniable tactical success thanks to the skilful use of artillery and tanks, a success only marred by a German counter-attack which restored the front line–which shows that the Germans were just as capable of overcoming defences as the British.
The Germans enjoyed even more success in 1918, when their Spring Offensive, or Kaiserschlacht (Kaiser’s battle), succeeded in finally breaking the stalemate and throwing the Allies back more than 60 miles. The remainder of the war, with far more mobile fighting, saw numerous examples of defences being overcome (although these defences tended to be far less well-prepared than they had been during the stalemate).
So trench-storming was often successful; in fact, you’d struggle to find an offensive which didn’t achieve at least some tactical success. The natural question, then, is: why didn’t the Allies achieve an operational breakthrough if they were able to capture the German trenches virtually every time they launched an offensive? The answer is in the poor state of communications. To have any chance of exploiting a breach, commanders had to hold back reserves until the time was right; sending them in too early would lead to casualties from the enemy artillery, and allow the troops to become disorganised by enemy action and the destroyed terrain. Commanders had to wait for confirmation of a breakthrough before committing their reserves, for if they were used poorly, and came up against enemy defences, their attack would peter out before they had created a large enough breach in the enemy line to form the basis of a break-out operation. News of a breach, however, was extremely difficult to send back; troops lacked radios, telephone lines were quickly cut by artillery fire, and the only alternative was to send a runner, who, if they did make it back to HQ, would take, on average, about 12 hours to do so. The defenders, meanwhile, would be busy reforming their defensive line, which would invariably take far less time. Armies of the time simply lacked the technology needed to react quickly enough to take advantage of breaches, apart from when tactical success was so overwhelming (as in the 1918 German Spring Offensive) that the defenders were incapable of reforming. The need to rely on horse-drawn transport also made the movement of troops slow. By 1939, armies had both portable radios and far more motor transport, which is why World War Two never really became a stalemate like World War One.
There’s a tendency to assume that, since the Western Front was for so long an operational stalemate, this was reflected at a tactical level too. The truth is that trench storming was often successful; no defensive system was safe from assault, as the numerous successful attacks on the extremely advanced Hindenburg Line prove.
Casualties during World War One were extremely high, especially during offensives. Unfortunately I don’t have any statistics, but suffice to say that they would be well into the tens of thousands for major offensives. It’s important to note, however, that casualties were always several times higher (at least) in the mobile periods of the war; trench warfare was relatively safe in comparison. Men in the trenches were not always being shelled in some kind of perpetual battle; on the contrary, on quiet sectors of the front an unofficial true existed between the two sides, with the soldiers doing only what fighting was necessary to placate their commanders, and otherwise trying to co-exist with the enemy (for more see Tony Ashworth, Trench Warfare 1914-1918: The Live and Let Live System (London, 1980)) It’s also worth noting that World War One wasn’t necessarily more bloody than World War Two; a British soldier was more likely to become a casualty in Normandy in 1944 than on the Somme in 1916 or at Passchendaele in 1917.
Trenches were often taken by assault. The reason everyone thinks they weren’t, is because tactical successes were only rarely turned into operational and strategic successes due to the limitations of battlefield communication at the time.
[It wasn’t the tactics of trench-storming that were lacking, but rather the ability of either side to exploit successful breakthroughs. The defender had the capability to rapidly reinforce depleted sectors via railroads, while attackers had to move forward on foot. The density of soldiers on the Western front and a lack of mechanization made attempts at maneuver warfare futile.]
* Tactical level=involving squads and companies. Operational level=involving units up to divisional size. Strategic level=involving armies.
Sources: •Paddy Griffith, Battle Tactics of the Western Front: The British Army’s Art of Attack 1916-18 (London, 1994). •Robert M. Citino, Blitzkrieg to Desert Storm: The Evolution of Operational Warfare (Lawrence, 2004). (Citino discusses the limitations of operations in WWI in his introduction). •Tim Travers, The Killing Ground: The British Army, The Western Front and the Emergence of Modern War 1900-1918 (Barnsley,  2003). •University lectures and seminars and general reading.