Does the Navy use fission or fusion reactors aboard their subs and carriers?

I know most nuclear reactors are powered through the fission of an isotope of Uranium 238, however, I have read somewhere about fusion reactors which fuse together Hydrogen atoms, eventually creating Beryllium 6 which decays to produce the heat. Has the Navy started using this model of reactor yet? I was just wondering, because I'm going to boot camp next month and I'm going into the nuclear power program. Thanks.