What was the plan in the battle of the somme?

the french and the British dropped bombs on the German trench's to try and kill the Nazi's but the Germans had buried trenches underground so very little got hurt and the barbed wire at the front of the Nazi trenches was not cut so when the whistle blew and the Brits ran out the Germans set up there machine guns and killed them and the ones who made it the barbed wire was not cut so they had no chance of survival