Final answer:
The longest Marine engagement of World War II was the Battle of Okinawa, which lasted from April to July 1945, with intense fighting and heavy losses on both sides.
Step-by-step explanation:
The longest Marine engagement of World War II was the Battle of Okinawa. The battle raged from April 1945 well into July 1945 and was the most intense and bloodiest battle of the Pacific theater. Over the course of this engagement, American forces faced fierce Japanese resistance with heavy losses on both sides, including over 180,000 U.S. Army soldiers and Marines encountering a well-entrenched Japanese army for a span of two and a half months. This battle was crucial as it provided a strategic location for the potential Allied invasion of Japan. The Battle of Guadalcanal, while extended over six months, was not as lengthy as the Battle of Okinawa.
Answer: C. Battle of Okinawa