During the funeral for one, I found out that two of my best friends were among the marines who fought in Iwo Jima. My friend Joe was being buried in the military section of the cemetery when I remarked to the other friend that I never knew Joe was in the military. My friend Jim said both he and Joe were in the marines and were part of the force that fought at Iwo Jima. He said when you’ve been in those bloody assaults, you don’t talk about it.
Fixed it for you. When refering to United States Marines or the Marine Corps the term "Marine" is a proper noun and should always be capitalized.