Submarine-launched ballistic missiles are the traditional, but very expensive, method of providing a second strike capability, though they need to be supported by a reliable method of identifying who the attacker is. Using SLBMs as a second-strike capability has a serious problem, because in retaliation for a submarine-launched ICBM, the wrong country could be targeted, and can cause a conflict to escalate. However, implementation of second strikes is crucial to deter a first strike. Countries with nuclear weapons make it their primary purpose to convince their opponents that a first strike is not worth facing a second strike. Such countries have many diverse launch mechanisms, prepared responses to various nuclear attack scenarios, launch mechanisms in many different areas of the country, and underground launch facilities that are specifically designed to withstand a nuclear attack.