Can't fire nukes

[hucker]

I have a submarine. I have two nuclear devices I got from someone else when a world congress made everyone have equal amounts. I have never built my own nuclear device but the option is there if I had some uranium. I have completed nuclear fission and built the Manhattan project. Why can I not fire those nukes with the submarine? The icon to launch them isn't there when I select the submarine. The submarine is only about 5 tiles from someone I'm at war with.