Complex sentence: On the left bank of the Tigris, this would mean swinging wide around the Turkish defenses and marching at least 30 miles through the desert and then relying on the Shatt al Hai for their communications and then linking up with the Kut garrison.
Split into simpler sentences: On the left bank of the Tigris, this would mean swinging wide around the Turkish defenses and marching at least 30 miles through the desert. Then, relying on the Shatt al Hai for their communications, the force would break through the Turkish lines and link up with the Kut garrison.