Complex sentence: The Holt tractors were a range of caterpillar tractors built by the Holt Manufacturing Company and famously used by the British and American armies in world war I for hauling heavy artillery: including BL 9.2 inch Howitzer and the 8 inch Howitzer Mk 1.
Split into simpler sentences: The Holt tractors were a range of caterpillar tractors built by the Holt Manufacturing Company. They were most famously used by the British and American armies in world war I for hauling heavy artillery: including BL 9.2 inch Howitzer and the 8 inch Howitzer Mk 1.