Complex sentence: Once in the combat area the 2nd Mixed Brigade attacked the rebel armies in Sierra Trapera and in Mocitas-Mataborrachas and within the height of the battle it was sent towards the inner area of the pocket in order to cover the withdrawal of the trapped Republican units.
Split into simpler sentences: Once in the combat area the 2nd Mixed Brigade attacked the rebel armies in Sierra Trapera and in Mocitas-Mataborrachas. In the height of the battle it was sent towards the inner area of the pocket in order to cover the withdrawal of the trapped Republican units.