Since 2006 U.S. SOCOM (Special Operations Command) has been seeking a new terrain following radar (TFR) for its smaller aircraft (MH-47G, MH-60M, MC-130H and CV-22) that would enable safe flight at very low (under 40 meters) altitudes. TFR uses radar and other sensors and electronics to enable aircraft to safely fly very close to the ground at night and in bad weather. This is a major combat advantage because the low flying makes you less observable by enemy radar, or eyeballs and ears. This sort of flying has become more frequently necessary for quickly getting into areas undetected. Previously TFR equipment with these capabilities was too bulky and heavy for these smaller helicopters. Since the 1990s the weight, size and cost of TFR components has come way down while reliability has improved.
TFR also requires a reliable flight control system, because, at those altitudes (sometimes under a 40 meters), flight adjustments have to be made automatically, without any pilot intervention. The first TFR was used during the 1960s, by the U.S. F-111 fighter bomber. TFR has since been adopted by several other aircraft, like the Tornado IDS, Rafale, F-15E, Mirage F-1 and B-1B. The basic TFR technology, ground mapping radar, was developed and used during World War II.
Putting together the new lightweight TFR was to cost SOCOM less than $200 million. In 2006 SOCOM funded a competition between a modified version of the existing APN-241 TFR and a new APQ-187 Silent Knight. At first the APN-241 seemed like the best choice but by 2013 field tests demonstrated the APN-241 would not work and to fix that would, in effect, mean developing a new radar. The APQ-187 now looked like the better option and six were ordered for field testing.
Such equipment will also have some commercial use (aerial ambulances, police and rescue squads), who have to respond in bad weather or night. TFR also provides more detailed information on the weather, and details of what's on the ground below, both of which are also advantageous. Silent Knight looks good but there are still technical problems that have to be resolved and tested. If all that is successful a new TFR should be in service by 2020. SOCOM needs about 220 of these new TFR systems (69 for the MH-47G, 72 for MH-60M, 50 for CV-22, and 20 for MC-130H).