Where is my uranium? Is this a bug?

[ZeroOne]

I'm playing a game (standard size archipelago map, warlord difficulty) where I have advanced to the point that I have discovered Physics and got Uranium revealed. I have several sources of uranium and I have built mines on top of them. Still, I cannot build Destroyers or Transports -- they are grayed out because they "require oil or uranium". Why might this be happening?

I'm sure there's a perfectly reasonable explanation for this, but I just cannot figure out why uranium is not shown on my cities. I have attached a screen shot of a city with uranium within its radius and another one of my current technology tree.

 

[6K Man]

You need Fission to take advantage of Uranium

 

[ZeroOne]

Oh, thanks 6K Man! It was too obvious... Now that you mention it, it does say in the Civilopedia that Fission enables it... I just thought it meant that it enables me to research Fission, but obviously it couldn't be so. Thanks again!