Everybody knows GPS, that satellite navigation system that allows even phones to determine the location with a few metres inaccuracy, and centimetres for military-grade GPS receivers (similar for Galileo, Glonass). It sure allowed for many new and relatively cheap guided munitions, made positioning for indirect fire weapons and ships on oceans much easier and also enabled systems such as Blue Force tracker, which help troops to stay aware of where comrades and subordinates or simply off-limits locations such as hospitals are.
Less well-known are inertial navigation systems (INS), even though they're older. It began with big, heavy and expensive black boxes like this (LN3)
|LN3-2A, (c) Klu andre at en.wikipedia|
and now we're down to this
and "This" actually includes a GPS receiver as well. It doesn't use the most accurate INS technology, though. Currently an error of 5 metres after one minute is achievable with such MEMS technology.
Such miniaturisation (and cost reduction) isn't uncommon; it happens often that new technologies are first used on ships (if heavy and bulky) or airplanes (if price is the greatest problem), then descend towards tanks and finally become portable. We've had this with radios already, and hard-kill active protection systems appear to follow a similar route.
INS already made it down to chip size, weight and cost - and thus qualifies for use in munitions even.
The accuracy of guided munitions can be summarized like this:
semi active laser (SAL) > GPS > INS
The combination of SAL + GPS + INS appears to become a widespread choice in guided munitions, in which SAL is only available if someone can illuminate the target (suitable for moving targets), GPS is sufficient for hitting stationary targets and INS is the backup to GPS in case GPS fails due to jamming.
So even perfect GPS jamming will only increase the CEP (circular error probable, a metric for shot dispersion) modestly.
The small size and low cost of modern INS is beginning to make itself felt, for such chips have been available for a few years only and development cycles for munitions and drones are frustratingly long.
We'll likely see such chips in individual infantry (and even more so scout) equipment, and even in perfect GPS/Galileo/Glonass conditions future troops may receive timely warning of incoming threats because their personal radio received a warning message and the navigation by INS allowed some tiny central computer chip to determine that the warning was relevant, creating an audio warning with the headphones.