During the 16th - 18th centuries during siege warfare the attacker would build increasingly complex siege lines that would approach the enemy over the course of days, weeks, and months until they were able to become close enough and do enough damage to the fortifications and capitulate the enemy. The trenches in the beginning of the war (Western Front) were very simple as they developed from small foxholes and simple dugouts. I was wondering what made it impossible to dig lines towards the enemy on a diagonal similar to how earlier European sieges took place. I realize that artillery was more accurate and devastating and I also know that most World War I generals and their officers were much more intelligent and competent than they're usually made out to be.
So what made the older siege line technique impossible?
This was in fact done quite a lot.
You can view very detailed trench maps at this site from which you can clearly see many examples of such saps being dug towards the enemy position.
Another example here around Gommecourt also clearly shows German saps extending towards the British trenches.
The question of course is what would you hope to achieve by the extensive digging of saps very close to the enemy?
If you were to dig a sap close enough to the enemy that you could do damage to him (presumably by lobbing grenades into his trench) then you would be close enough for the enemy to lob grenades into your sap. In fact, both Junger in Storm of Steel and Rommel in Infantry Attacks record grenade fights raging between opposing sections of trench which were very close together.
You would not be able to launch a large scale attacks from a sap as it would not be possible to move a large number of men in a short period of time towards to the enemy.
So this was in fact done, but they had limited utility.
Far more useful was the ability to excavate a significant network of tunnels, particularly in areas where chalky soil predominates.
Examples of such tunnels are preserved around the Vimy memorial. Lit with electricity, they enabled men to move around unobserved and unmolested by enemy fire. In the Champagne (Marne/Aisne) large caverns could be excavated to serve as depots, barracks, hospitals or even schools.
Another ancient technique was to dig mines under the enemy position, fill them with explosives, and detonate them immediately prior to an attack. The craters from such mines are still visible, of particular note being the Lochnager crater.
Detonated on the 1st day of the Somme, the effect was predictably devastating, but mining takes an awfully long time, and no matter how initially devastating, mines did nothing to solve the problems that lead to the coagulation of the front lines in the first place.
