Ring-laser INS still have a drift of a few kilometres per hour.<p>To keep their respective INS in-check, Tomahawk looks <i>down</i> and performs terrain-comparison whereas Trident looks <i>up</i> and does stellar nav...<p>The Kearfott Mk 6 that is used by Trident is the successor a line of stellar nav units they produced for the Navajo, SR-71, Hound Dog and FB-111.  And probably a bunch of others I&#x27;ve forgotten.<p>The early models used a sheath of acetate star-chart sheets in a mechanical loader to perform the matching operation!