Someone on another thread postulated that this photo may have been "Photoshopped" to produce the picture of Kerry in the same shot as Alston. I believe that idea was discounted, but I'm not so sure. In the photo, Kerry himself appears completely detached from the rest of the subjects; as if he's not even aware of them, or them of him. Look, too, at that weird object upon which Kerry's elbow is resting. What is it? If you enlarge it, it appears to be a formless mass that simply melds into the background. Very suspicious, in my opinion.
The "formless blob" appears to be a mounted gun under a tarp. Probably a .50 with a small armored shield -- (the pointy object to the left of Kerry's elbow.)
The aft gun mount with a cover over it? You can see the .50 cartridges in belts below the "mass". The mount was a unique over/under design with a M2 .50BMG machine gun mounted coaxially with an 80 mm mortar, that was "trigger fired" rather than fired by the round being dropped into the muzzle. It was still loaded from the muzzle end however.
I have to agree with the others concerning the tarp covered gun but the one thing that stands out to me is the angle of the shadows. Kerry and the guy standing next to him have shadows that make the sun appear to be up and over their left shoulders while the other three more directly up and to the right.
Also, again notice the angle of view for Kerry and the guy next to him as compared to the other three. I could be wrong but those features of this photo stand out more then anything else if this photo is to be considered bogus.
Note the shadows. The shadows on the other crewman all look like the Sun is coming from the left, EXCEPT for Kerry, where HIS facial shadow is cast in the OPPOSITE direction.
Look, too, at that weird object upon which Kerry's elbow is resting. What is it? If you enlarge it, it appears to be a formless mass that simply melds into the background.