Robot Nemesis by E.E. "Doc" Smith

The War of the Planets ended in stalemate. Both fleets were so horribly shattered that the survivors despaired of continuing hostilities. Instead, the few and crippled remaining vessels of each force limped into some sort of formation and returned to their various planetary bases. And, so far, there has not been another battle. Neither side dares attack the other; each is waiting for the development of some super-weapon which will give it the overwhelming advantage...