Complex sentence: The 105 mm M2A1 (M101A1) howitzer was the standard light field howitzer for the United States in World War II, seeing action in both the European and Pacific theaters.
Split into simpler sentences: The 105 mm M2A1 (M101A1) howitzer was a howitzer developed and used by the United States. It was the standard U.S. light field howitzer in World War II and saw action in both the European and Pacific theaters.