It could be that the GTA envisioned an end to the war by launching Harbingers from say an Orion onto the surface of Vasuda Prime. However, bombs can be tracked and easily shot down, although this in itself is a disadvantage, as we've seen that if a Harbinger is shot, the shockwave and no doubt radiation fall out will be massive. Additionally, I doubt very much an Orion will be able to get that close to the planet without being shot down by Vasudan forces
So therefore, I believe that the plan was to force their way into Vasuda Prime system eliminating any space based defence forces, and then to bombard Vausuda from above. However, considering we never got that far before the cease-fire was signed, the bombs were put into storage until time dictated that they were needed.