They are Marines taking sniper fire, the Marine taking the pics is well known for these photos, They did an article in Leatherneck Magazine on him. It shows a Corpsman trying to rescue a fellow marine while doing this another marine gets hit by the sniper he runs back to help him. The other marines all lay down fire on the marine and eventually save one of the marines. One was killed but the other made it out.
Hope that helps would give you the specifics but i lost the magazine somewhere.