MIRVs and the Strategic Balance

Abstract

MATHEMATICAL models are a useful aid in describing the strategic balance of deterrence, but must be used with caution. Bellany¹ uses a model to show that, in certain circumstances, the fitting of multiple independently targetable re-entry vehicles (MIRVs) instead of single warheads on intercontinental ballistic missiles may make the strategic balance more stable. He calculates the number of warheads X_b belonging to side B which would survive a first strike by side A and could then be used against A's cities in a retaliatory second strike. N_b is the number of launchers possessed by B, each with reliability R_b, and with n_b warheads. A fraction f of A's N_a missiles are used for a first strike, and each of the n_a warheads has a probability C_a of destroying one of B's launchers. By assuming a situation in which A and B have identical parameters he obtains a simple expression which can be maximized with respect to n. For plausible values of the parameters, the value of n corresponding to maximum X is greater than 1.