The guidance systems had to account for local variations in gravity as the missile flew to its target. One of the reasons ballistic missile accuracy improved so

The guidance systems had to account for local variations in gravity as the missile flew to its target. One of the reasons ballistic missile accuracy improved so much was that measurements and mapping of these local anomalies improved so much. Most are due to magma reservoirs or large mineral deposits. Some are well-known in their effect, but their specific cause is still unknown: https://eos.org/science-updates/seismologists-search-for-the-indian-oceans-missing-mass https://eos.org/science-updates/seismologists-search-for-the...