Distorted UV unwrap issue I am trying to UV unwrap a model of a tank I am creating. I am having an issue trying to unwrap the tank body. It is basically a box with a curved front and back. I am trying to do a seamless texture all the way around, so I split the body in half so that I could unwrap it, then duplicate it and flip it so the UV coordinates are mirrored. When I press 'u' and select "Unwrap," I get the following result:



As you can see, it's a continuous row of quads with two open ends, so I see no reason why it shouldn't unwrap in a more straightforward fashion. I looked around for solutions already. I tried applying the scale, which made no difference. I tried resetting the UVs from the 'u' menu, then unwrapping again, but that still resulted in distortion. I already removed doubles. I would set up some seams, but given the shape I have I don't see how that would help at all. Maybe if I re-created the geometry it would work, but then I don't understand how it would get stuck in this state.

How can I unwrap this so that each face keeps the correct proportions and the edges are aligned to X and Y in the UV editor?

Here is the blender file if that helps: simple tank (unwrapped).blend

Thanks.
You have pinned vertices. Here are two images which describe how to fix the issue.