Staged Thermonuclear weapons traditionally have used a Fission-Fusion design, or even a three-staged Fission-Fusion-Fission design. However, there is theoretically no limit on the number of stages you can add; five or six and you can hit a Gigaton yield (compare that to 50 Mt; the largest nuclear weapon detonated). A direct hull hit and that's some serious kinetic and thermal energy, even if the majority is wasted.
Or, one could make a shaped charged by surrounding the core with fission detonators, both compressing the core but also directing the resulting fissioning material.