June 29, 2011:
As the cost of jet fighters keeps rising, air forces have to come up with ways to control the costs. One increasingly popular method is putting specialized (and not-always-needed) electronics into a pod (that can hang from the wing), rather than building it into the fuselage of the aircraft. One application of this (missile warning systems), is growing in popularity. For example, Denmark and Norway have bought the PIDS (Pylon Integrated Dispensing System) system, which is two bomb like pods, one carried under each wing of an F-16. The PIDS pod contains the missile detectors, and the chaff and flares that will be deployed to neutralize the missiles.
For most air forces, that only expect to send a few of their aircraft into combat at any time (as has happened with many NATO nations recently in Afghanistan and Libya), huge savings can be had by only having PIDS pods for a small percentage of their fighters. These would be used regularly (moving to other aircraft as needed) for training, then taken with aircraft sent to a combat zone.
Similar pods are available for helicopters (like gunships, that have stub wings to hang the pods from) and larger UAVs. For each type of aircraft supported, there has to be some new software and wiring changes for the aircraft, so that the pilot can operate the pod, and use the information the pod sensors detect.