Complex sentence: The M1918 was similar to most mobile siege cannons of World War One and with the exception of the caliber and a few minor details is an exact copy of the French 280 mm howitzer.
Split into simpler sentences: The M1918 was similar to most mobile siege cannons of World War One. With the exception of the caliber and a few minor details, it is an exact copy of the French 280 mm howitzer.