Tritium enhances the yield of a fission bomb via injection into the core if my source is to be believed, the book: “The Fear of All Sums”.
I didn’t see where they were trying to achieve fusion.
One can boost the yield of a fission nuke by an order of magnitude by injecting tritium and deuterium into the core. The hydrogen isotopes fuse and release high energy neutrons which induces more fission.