The U.S. Navy is equipping its F-18E fighters with IRST (Infa-Red Search & Track). IRST uses a high resolution infrared (heat sensing) radar to positively spot and identify a potential aerial target (using a 3-D model of the target in its computer memory.) This is similar to the ATFLIR (Advanced Targeting Forward Looking Infrared) pods used to spot surface targets.
FLIR (Forward Looking Infrared Radar) has been around since the 1980s, and as the technology became more powerful, it was possible to spot and identify targets at longer ranges. The ATFLIR can identify ground targets from 20 kilometers away. It soon became possible to use FLIR, in the form of IRST, as a sensor for spotting aircraft. This was a big advantage, because FLIR is passive. It doesn't broadcast, like normal radar, thus the target cannot detect those radar transmissions, and be alerted that it is being "painted" by a hostile radar.
IRST has its limitations. The main ones are range (about 30 kilometers) and problems with clouds and have distorting the heat signature of the target. The short range means that another aircraft using its radar (which has a range of over 100 kilometers) has an obvious edge. The distortion problems are slowly being solved by improved computer analysis of the detect image. Since many warplanes like to operate "quiet" (without any electronic transmissions), IRST becomes the best way to spot the other guy, and open fire, first. IRST is also capable to spotting stealth aircraft, which are protected from radar transmissions, but still have jet engines throwing off lots of heat.
The F-18E IRST will be mounted in a modified centerline drop tank, which will contain the IRST as well as 68 percent of the usual fuel. One problem with this approach is that the F-18E can't jettison this drop tank, to make itself more maneuverable for air-to-air combat. Other aircraft, like the F-22 and F-35, have the IRST built into the fuselage.
Pilots have already found that they could use their targeting pods for spotting aircraft, which prompted air forces to hustle up the equipping more aircraft with IRST (which is designed especially to spot other aircraft, but can also be used to detect surface, land or sea, targets.)