The four navigation layers of a Tomahawk, and what defeats each one
| System | What it senses | Typical accuracy | Jam-resistant? | Limitation |
|---|---|---|---|---|
| Inertial navigation (INS) | Its own acceleration and rotation, using gyros and accelerometers | Error grows continuously with time and distance flown | Completely immune — it receives nothing | Drift is unavoidable. Left alone on a 1,000-mile flight it misses by miles |
| TERCOM | Ground elevation under the missile, via radar altimeter | About 80 m CEP in the TAINS configuration | Immune — passive, no signal to jam | Needs terrain relief. Useless over water and nearly useless over flat desert |
| GPS | Timing signals from navigation satellites | Metre class in clear conditions | No — a low-power ground jammer defeats it | Depends entirely on a signal that arrives weaker than background noise |
| DSMAC | An optical image of the ground, matched to a reference scene | About 10 m CEP | Immune — passive, no signal to jam | Needs the right light, season and contrast. Scenes must be prepared in advance |
Sources: Directory of U.S. Military Rockets and Missiles (Andreas Parsch); Irani & Christ, Johns Hopkins APL Technical Digest 15(3), 1994; US GAO, NSIAD-95-116. CEP figures are for the Tomahawk family and vary by block.