On "jamming" cruise missiles ...
US cruise missiles use a combined GPS/INS system. They get GPS signals, but they also have an inertial navigation system (INS). The two systems compliment each other. GPS is low-bias and high-noise, INS is high-bias and low-noise, put them together, you get a low-bias low-noise system
How does one jam GPS? Two ways. There are noise generators, that just flood the GPS frequencies with static. If the missile loses the GPS signal for any reason, it keeps flying on INS alone. Any INS will drift away from true over time, but it takes significant time for a significant drift. If the jammer is just at the airbase, that's just a few seconds of signal loss, so no significant drift.
There are also spoofers, which receive the incoming GPS signal, delay it a few microseconds, and rebroadcast it at a higher power. You don't have to know the GPS crypto codes for that, as you're not decoding the signal, you're just rebroadcasting it. Since the decoded GPS position depends on the time delay of the signal, that would cause an erroneous position calculation if a GPS receiver used the spoofed signal. A "dumb" GPS (like every consumer model) will be fooled by such things. You can bet Tomahawks have much smarter GPS units, smart enough to know not to lock on to a spoofed signal just because it's present and very strong.
