I've altered the range envelopes in SRBM, MRBM, IRBM, and ICBM for consistency. I chose to conform to the U.S. Missile Defense Agency's definitions of these classes of missiles, which are in common use in the U.S. Defense Department and the defense contractor community. The range boundaries are partially based on international treaties (e.g. the INF Treaty), but like any system of classifying missiles by their ranges, it is also somewhat subjective and arbitrary. For example, an SRBM with a sufficiently lightweight payload can achieve MRBM range, and an IRBM could be used to place a very small payload in orbit ("infinite" range). Conversely, an MRBM with too heavy a payload may not exceed 1,000km. To be totally correct we would need to state that a missile system's range is calculated by assuming the mass of its most probable payload.