How about successful, rather than failed deterrents? Most prewar war / early war stuff is what failed to convince the other guy not to fight, how about gear that is so ludicrously capable, so totally over matched what the other side had, that they decided to be friends instead of enemies? Bolo
but other over matched sort of stuff too.
Maybe a milder type too, i.e. the overmatch the RAF claimed they had when they were convincing the British Government to fund the RAF bomber force over the Army and Navy but was shown to be an illusion at Munich is actually real, in that they actually have the capability they claimed.