Why active Trench warfare in WW1?

Excellent answer here.  The real problem was lack of movement allowing any form of true tactical decision.  That was only overcome with the advent of motorized tracked vehicles that could push through trench lines and barb wire as well.

That is why the first 'tanks' looked so odd.  They needed to block bullets and move forward and a machine gun was helpful.  They also worked and ended trench warfare then and there as the dominate tactic.

In fact the next serious episode of trench warfare only occurred again in Korea when political considerations locked the line and everyone knew it..

Why in WW1 did soldiers both British and German run straight to enemy held positions and get mowed down in their thousands? Wouldn’t it have been more sensible to wait in the trenches for the other side to attack?

Stephen Tempest, qualified amateur historian

Here's the big secret that popular history doesn't tell you: most of those attacks on the enemy trenches succeeded.

The reason why the war was deadlocked for so long was because as soon as one side captured the enemy front line, the enemy would just counter-attack and take it back again. The fighting could go backwards and forwards for weeks over the same small patch of ground.

All the mud and barbed wire and trenches meant that the attacker moved forward very slowly, and normally needed to pre-plan the attack carefully. Mountains of artillery shells would be stockpiled behind the lines, and weeks of the country's ammunition production might be fired off in a day or two, so major attacks were infrequent.

The trouble was that the defender could bring up reinforcements by rail faster than the attacking troops could slog through the mud to capture their trenches. Worse, as the war went on the front lines became more and more heavily fortified, with multiple defence lines, so that capturing the first simply meant you now had to attack the second, against a fully alert and reinforced enemy.

So why not simply wait in the trenches and let the enemy attack you? Several reasons.

First, as Miran Miljak points out, that means surrendering the initiative and allowing the enemy to attack you at a point of their choosing. If you, as the attacker, are fully confident that the enemy will simply sit in his own trenches and never leave them, you don't need to keep more than a token force defending your own trenches. Instead, you can concentrate most of your army against a small section of the enemy front line, and attack there with crushing numerical superiority.

The experience of recent wars, such as the Russo-Japanese War of 1904-05, seemed to indicate that despite the strengthening of the defensive through the introduction of barbed wire, machine guns and rapid-firing artillery, the attacker would almost always win the battle as long as they were determined enough and willing to accept casualties. The attacker chooses the time and place of their attack; the defender can only react to them.

Second, there's the question of morale. Taking part in a major offensive might be terrifying, but at least you're doing something. You're attacking the enemy to do them harm, and if the attack succeeds, you're bringing the end of the war nearer. But what if you're just sitting in a muddy hole in the ground for months on end, never firing your rifle?

You'll still be suffering heavy casualties, because most of the deaths in the First World War came from artillery, not machine guns. But you'll never see the enemy that kills you: just hear the whistle of the shells, the explosions, and the screams of the mutilated and dying. And those deaths will be apparently useless, because you're not doing anything to win the war sat there in your trench. You're just waiting for death.

The same applies at a larger scale to the generals in command. The war is costing the country billions in lost production and increased costs even if you ignore the effects of actual war damage. Every day that passes without a victory racks up more debt and more death. How will the politicians react to a general who just sits there, day after day, month after month, not actually doing anything except claiming, "I'm waiting for the enemy to attack"?

During the American Civil War, President Lincoln got so frustrated with the lack of activity by General George McClellan that he wrote him a letter saying, "If General McClellan does not want to use the army, I would like to borrow it for a time." Eventually, McClellan was fired and replaced... but he was far more proactive than what is being proposed here.