One of the biggest changes in the way land battles were fought during WWII was the use of radio.
In WWI trench lines along the front were connected to HHQ (higher headquarters) via wires and telegraphy. (Behind the lines HQ were interconnected by telephones.) Once troops went "over the top" in an attack, there could be little or no communication between the troops at the sharp end, and those responsible for planning the battle. There could be millions of casualties between when an attack failed and the survivors straggled back, or were pushed back to the original lines.
In WWII, scouts and reconnaissance patrols could message back information on the location of enemy troops in real time, without having to return to friendly lines. More important, company level commanders could use radios to inform HHQ that the planned attack had failed to survive contact with the enemy--and the generals could either call the attack off and call the troops back, or more usually adjust plans to deal with an enemy unit that wasn't where it was expected to be.
Look at the invasion of Normandy for dozens of examples of this. And a few, like the Falaise Gap, where inability to change a boundary between US and British troops quickly, allowed German troops to escape. I used to have friendly discussions of that particular issue with a US Army Intelligence Major who thought that Montgomery could not have overcome the British doctrine. My feeling was that he should have "stood up" and taken the risk that his troops might have started shooting at American soldiers as the gap closed. In either case, the issue was the "decision loop." Should Montgomery have let Patton move into "British" areas of the battle before Montgomery could get word back from his field commanders about where they were and agreeing to the changes? Patton knew where the British were from US Army AF planes attacking Germans in the gap. But Montgomery did not have access to similar real-time information.
Of course, if Montgomery behaved like Patton, and commanded from the front, he would have known where the front was. ;-) That was not British doctrine at the time, and was not how Americans (or Germans) were taught either at the time. But Guderian and Rommel taught Patton, and he was a very apt pupil. The decision loop that mattered the most was with your armor, and if you were with them, that kept it as short as possible. ;-)
Of course, doing that required radio contact between the general and his headquarters. Staff there could manage all the other details--but getting your armor to where it was needed NOW, was decisive.
