A very good book on this exact topic would be "Les vainqueurs" ("The Winners") by Michel Goya. He explains that by the end of 1917/early 1918 the French military has developed an entire culture of innovation and information sharing. Basically anyone with a half decent idea is given the means to try it out at small scale, and if it works then the idea is immediately shared, discussed and refined across the whole organization. Add to it that the country has entirely switched to a mechanized, heavily industrialized production, so much so that by mid-1918 the vast majority of all allied mechanized equipment is French-made. Chief among these were trucks - lots and lots of them. If anything, warfare really entered the XXth century around that time.

Pétain is famously quoted as saying in 1917 "I am waiting for the Americans and tanks", which today would be understood as the former bringing the latter. But in fact he started entirely reorganizing and modernizing the way the military worked, and just needed fresh troops to backup the more battle-hardened ones he later sent to push through the crumbling German military.

On the German side, peace on the Russian front by Fall 1917 meant that tons of experienced shock troops were made available for the massive Spring 1918 offensive(s). But once these were contained pretty much all of the energy was spent, and it was time for the now overequipped allies to roll.

At the end of the book he very much contrasts the French culture of bottom-up innovation with the top-heavy one that prevailed in the mid to late 30s and led to defeat: at the end of WWI officers were promoted based on the number of publications on new ideas and concepts they would make, whereas 20 years later the same proactive attitude would be a negative for their advancement.

It’s not really correct to infer that there was an enormous change between the last months of 1917 and the first months of 1918.

What did happen was the coming together of a large number of technological and tactical innovations that allowed the problems posed by trench warfare to be finally overcome (and this had happened by Cambrai in the autumn of 1917, albeit at the tail end of the campaigning season).

To understand how the problem was overcome, we need to understand how the problem arose in the first place.

Firstly, The Western Front is quite constricted. The theatre of operations only stretches from Ypres to Verdun, and advances in logistics, canned food, medicine and hygiene meant that million man armies could be deployed en masse and kept in the field indefinitely. Thus, in a small area, there were anything up to 8 million men at arms facing each other. Enough to make for a continuous and uninterrupted siege defence with no flanks, meaning any assault had to be frontal.

The lethality of artillery had increased dramatically since the Franco-Prussian war. The French 75mm field gun could fire as fast as a bolt action rifle. A battery could saturate a 4,000 square meter area with 75,000 shrapnel balls every minute meaning that if you wanted to hold a piece of ground and stay alive, you had to dig in, otherwise you would hold it dead.

Barbed wire effectively shut out cavalry, the traditional arm of exploitation and pursuit. While shrapnel firing field artillery was very good at killing men in the open, at the start of the war, it was very bad at cutting barbed wire and destroying fortifications, meaning huge numbers of guns were required for any assault which could consume literally millions of rounds of ammunition in a matter of hours.

The logistical challenge for the attacker was thus exponentially greater than the defender. Not only did the attacker have to stockpile vast quantities of munitions, but the overall shortage of guns meant that they would have to be moved from other sectors and relocated to attacking sector and it could take days just to dismantle and re-assemble large siege guns.

Once the initial attack went in, the attacker would have to move everything forward across the devastated earth of no man’s land, with no roads or railways, while the defender could reinforce on interior lines.

One further issue with artillery was that it took a long time to get the guns sighted in – the process of registering each gun gave the enemy plenty of notice of what was occurring, robbing the attacker of the element of surprise.

Lack of command, control, and coordination. Without radios, it was impossible for a General to find out what was happening in the attack. Reports would come in via runners, gallopers, carrier pigeons and whatever telegraph cables hadn’t been cut by artillery fire. The General had to make sense of a series of inaccurate, and often contradictory reports all of which were out of date by the time they were received. And once received, the difficulty in communicating new instructions to the front was almost insuperable.

Attacks therefore had to be made strictly according to a carefully timetabled and choreographed plan, with any variation spelling disaster. Of course, after the initial attack, everything would go pear-shaped. No plan survives first contact hence the law of diminishing returns. However successful the first stages of the attack, subsequent operations would degenerate into a series of expensive attritional slug-fests.

Furthermore, any new measure introduced to aid the offence was usually met with a parallel counter-measure in the defence. One of the best examples of this is the battles of Neuve Chappelle and Aubers Ridge in 1915.

At Neuve Chappelle, the British used a short but intense “hurricane” bombardment using mainly shrapnel shells before delivering the attack. In this case, the bombardment was enough to sufficiently demolish the German fortifications while the sudden and intense violence of the shelling sufficiently suppressed the defenders and the initial attack was highly successful.

However, at Aubers Ridge, the Germans had improved their fortifications. In this case, the German wire was uncut and the British infantry were cut down in droves with their dead lying thick on the ground often only yards from their own trenches. It was an unmitigated disaster. The costliest battle ever fought by a British army to date had achieved no territorial gains at all and had inflicted minimal casualties on the enemy.

Such was the nature of the war. And thus, the history of the western front is the history of how the armies attempted to overcome these problems.

One of the options favoured by the British was to take the ‘indirect approach’ and circumvent the western front by opening a new front elsewhere. Hence the campaigns in Salerno and Gallipoli. Both of which achieved little except the diversion of precious resources at huge cost in blood, treasure, and national prestige. The problems of the western front simply reappeared on the new fronts, but with exponentially worse logistical problems.

Extensive plans were also made to stage amphibious landings in Belgium to outflank the front (particularly as part of Third Ypres) but these plans never came to fruition.

The western front was therefore the decisive front. It could not be circumvented. It had to be attacked frontally. It had to be cracked.

The innovations made to overcome the problems on the western front included:

• High explosive was better at wire cutting than shrapnel, so production was switched to more HE.

• A vast expansion in the number of guns and shells, with a preponderance of heavy guns were to better destroy fortifications.

• Instantaneous fuses improved the wire cutting potential of HE.

• Flash spotting and sound ranging were developed to locate enemy batteries which could then be destroyed or neutralised

• Improvements in the ability of artillery to hit targets without registering fall of shot meant that bombardments could be shorter, more effective, and consume far less ammunition.

• Creeping barrages - attacking infantry would advance immediately behind a curtain of artillery shells which would suppress the enemy until the attacking infantry were literally on top of them.

• Better infantry/artillery cooperation through the use of SOS flares to target any holdups or enemy strongpoints, or retard or advance the barrage.

• Aerial spotting. Aircraft equipped with radio transmitters could observe the battlefield and communicate with artillery to better coordinate the attack.

• Tanks were useful in the initial stages of attacks, though they quickly broke down or were destroyed.

• Combat Air Support – the use of aircraft to directly support the attack using bombs and machine guns.

• Improvements in infantry firepower including the use of squad automatic weapons, hand grenades, rifle grenades, and the Stokes mortar. If the infantry could not always count on the artillery to provide fire support, they would take their own fire support with them

• Devolution of tactics to the platoon level to allow for small unit flexibility to out-flank and overcome local enemy strong points.

Arguably, the decisive factor in achieving victory in 1918 was not just the tactical and operational proficiency attained by the entente in combined-arms warfare, but the ability switch the axis of advance to a new sector meaning that the ability of the defender to reinforce on interior lines was effectively negated.