Birth Of A Symbol!

This little "schematic" of Captain America's shield covers a decent amount of ground for something apparently so simple in design. We learn both its weight and diameter; and while a 30-inch circumference sounds about right, it's a bit too wide a span to allow Steve Rogers to covertly strap on this thing underneath street clothes and appear as if he just has a broad back. But the shape resembling a tank's hatch cover makes sense, while also helping to blunt and disperse the impact of explosions or other forms of attack. (And it's a nice reference to Cap's wartime roots.)

The only odd part I couldn't quite get to make sense was the casting of the shield by Dr. MacLain, who must have begun his career in metallurgy in his early 20s if he's the same Dr. MacLain who later appeared in The Avengers. Yet, in that later tale, Adamantium is a completely new discovery, undergoing thorough testing for the first time:

As a result, the only way MacLain could have cast the shield as a mixture of Vibranium and Adamantium is if MacLain stumbled upon the second metal back in the '40s and didn't quite know what he was dealing with (and not even bothering to name it at the time). The Marvel Database specifies that MacLain created the shield using a Vibranium-iron alloy; but since MacLain was never able to duplicate the mixture of metals, perhaps there's a quantity of Adamantium in there and he simply doesn't recall how it was formed (or even what it was at the time). You'd think the man would have kept copious notes on what he was mixing every step of the way in the process--but glitches in the lab happen.