Complex sentence: After the first set-piece attack, unexpected delays slowed the tempo of operations, command was undermined by communication failures and infantry-artillery co-operation broke down, when the telephone system failed and the Germans had time to receive reinforcements and dig a new line.
Split into simpler sentences: After the first set-piece attack, unexpected delays slowed the tempo of operations command was undermined by communication failures. Infantry-artillery co-operation broke down when the telephone system ceased to work and the Germans had time to receive reinforcements and dig a new line.