Complex sentence: He therefore cancelled a second strike by heavy bombers scheduled for the afternoon of the first day in support of the advance towards the ridge, concerned that the 11th Armoured division should not be delayed by waiting for the strike.
Split into simpler sentences: He therefore cancelled a second attack by heavy bombers scheduled for the first afternoon. Although this was to be in direct support of the advance towards the ridge he was concerned that the 11th Armoured Division must not be delayed by waiting for the strike.