That rod is unguided unless you want that navy ship to send it kilometers off course. And all you need would be some island artificial or otherwise to mount some breaker guns. A cruiser can mount the breaker gun Array from skyword steel, but a frigate can mount the planetary defense Array in the revised core rule book. Presumably a suitable wet navy vessel could mount something similar. Wet navy vessels would be cheaper than space vessels. That said you wouldn't bother bombarding a seafaring vessel unless it was a threat like if it happens to be off the coast of your invasion target, in which case it is probably protected by land-side breaker guns.