Complex sentence: The 240 mm M1 howitzer was mounted on a slightly modified Heavy Tank T26E3 (later the "Heavy Tank M26 Pershing") chassis-it used an extra bogie wheel, to bring a total of seven.
Split into simpler sentences: The 240 mm M1 howitzer was mounted on a slightly modified Heavy Tank T26E3 (which entered service as the "Heavy Tank M26 Pershing") chassis. An extra bogie wheel was fitted, to bring a total of seven.