Complex sentence: The U.S. Army's official name for the unit was the 5307th Composite Unit (provisional), but visiting war correspondents, after viewing the 5307th's performance on the firing ranges, promptly dubbed the unit "Merrill's Marauders".
Split into simpler sentences: The U.S. Army's official name for the unit was the 5307th Composite Unit (provisional). Visiting war correspondents, after viewing the 5307th's performance on the firing ranges, promptly dubbed the unit "Merrill's Marauders".