The attached photo shows a MkXI PR Spitfire of the USAAF. Note that the front lower cowl seems to be rather bulged out. This is because the Mk XI Spitfires flew long distances and needed more engine oil capacity. This points out a unique design feature of the Spitfire. The lower cowl below the prop includes a section that is NOT merely cowling but the actual oil tank itself. They had to bulge that out to accommodate the extra oil capacity.
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