Can the President fire nuclear missiles without the approval of the Senate?

The President is the Commander In Chief of the US armed forces, and as such, he is fully empowered to make any decision and issue any order that he deems to be necessary to deal with a military threat to the US, and that would include firing nuclear missiles. If the US were under attack, that would not be a good time for the President to go to Congress and see if he can persuade them to authorize military action. However, the President can't declare war, on the Congress can do that. It may be that actually declaring war would be superfluous, if nuclear missiles were already fired.