JOE RIX
Steve is correct. It is the torpedo belt and I'm not quite sure why they felt they needed to mold it as a seperate part. It gives the hull a rather..well..interstellar appearance. I've given a lot of consideration as to if I need to do some extra work on it. It is not currently glued in place but, it might be fine once I do. Just another head scratching aspect of this kit.
NO, WAIT! FULL SPEED ASTERN! It won't fit any better than it looks now. I don't much remember the math, but it should be about 2" thick, which on the model is about 0.0025 ". This is the time to sand it WAY down. If you have a lower hull and plan to use it, glue the top and bottom together first.
So, you noticed that there's no belt on the lower hull? Seems odd for a torpedo belt.
Add that first using sheet styrene. I used 0.010. Thinnest I had. Then use that as a gauge to sand down the upper belt to match. I went back and squared up the edges with a razor blade. It also extends way too far astern. If you care, nows the time to fix that.
Actually I went a step further. Again, only for a full hull. The underwater hull is way too shallow draft. So I spliced in a layer of basswood to make up the difference. Then added the lower armor plates. Frankenship.
Oakland is Atlanta with new parts, including the 40 mm tubs in your photo in place of the original twin 5" gun houses. So it could be pops spread apart by years.