Complex sentence: The intense bombardment began at 04:00 and, 20 minutes later, all 16 guns of the machine gun company fired a barrage on the near face of the ridge, to lift as the infantry approached before continuing to fire on the reverse slope.
Split into simpler sentences: The intense bombardment began at 04:00 and 20 minutes later, all 16 guns of the machine gun company were firing a barrage on the near face of the ridge. They lifted their fire as the infantry approached before continuing to fire on the reverse slope.