target-findinS and horning devices devel-oped. for conventional mrnitions night be used. 95. To inprove long-range navigation, the i.nertial guidance systems vhich have long been used need to be supplenented by internittent, precise position in.forroation. This can be provid.ed. by a set of satellites in geostationary orbit as il-lustrated" e.g., by the United States Globa^l Positioning Systen (CpS) or Navigation System using Tine AnaI nange (NAVSIAR). For cruise missiles al]d. other low-flying vehicles, it is possible to scan the ground bel-ow ard. compare the results ith d.ata fiLed. in the computer memoxy of the vehicle. This coul-d be done by neasuring only the verbical profile of the Sround (e.g., Terrain Contour I4atching or TERCOM ) or by scanning some of its area properties (e.g' " Map Matching or IvM). 0f these techniques " GPS or NAVSTAI is said. to have been established but not depl-oyed, and there are reports of some technical difficulties regarding actual deploynent. TERC0M is weff advanced and MM still- experimental ' 97. For troming a weapon on the target, a m.mbex of sensols have been deveLopeal to govern the operations of steering mechanisms in the proJectile. These horning systens i.nclude a variety of radar, infrared and 18.ser devices' Sone of them coul,d. be ad.apted for use within strategic vehicles; others nay be used to enhaJrc e the accuracy of various tactical nuclear veapons ' To lrhat extent the nucl"ear- veapon States have already inplenented such options is not known, although nuclear-wespon States have not d.epfoyed guidsJrce systens for re-entry vehicles from ballistic missiLes , 98, Ad.vances in propulsion technology are also highly relevant for the evol"ution of nuclear forces, the nost recent exanple being the d evelopment of the cruise nissile. Jet-plopelfedo aerod.lmanic nissiles were first introduced in the Second