Pave Tack laser designators, an important feature that allowed the use of laser-guided bombs. A total of 92 F-4Ds were delivered, making this air force the main export customer for the "D" model. The F-4Ds were joined by 37 new-build F-4Es, ordered in the 1970s. The last of these was the 5,068th F-4 built in St. Louis. Under Operation Peace Pheasant these were delivered to the RoKaF 152 and 153 TFS (Tactical Fighter Squadron), 17th TFW at Chongju. This was only the beginning of South Korean F-4 acquisitions, as more ex-USAF F-4Es were delivered in the next few years, giving a total of 103 F-4Es. The South Koreans also received RF-4Cs. There were 12 ex-USAF 460 TRG (Tactical Reconnaissance Group, disbanded in 1990) that were sent to the South Korean 131st TRS (Tactical Reconnaissance Squadron), 39 TRG, at Suwon Air Base, along with another 11 sent later. ALQ-131 electronic countermeasures pods were also delivered. Overall, South Korea was one of the main customers of the F-4, with 216 delivered, including 60 "D" models, 55 "E" models and 18 RF-4Cs in service in 2000. Upgrades The South Korean Air Force has been quite satisfied with the F-4 and has carried out upgrades to extend their lifespan. A proposal made by DASA was evaluated that would have included installation of the APG-66 radar and AMRAAM missiles. This was equivalent to the Japanese F-4EJ KAI or German F-4 ICE, but the costs were too high for South Korea. The Air Force had already been forced to cancel an order for F-18s, which had been the winner of their new fighter competition and instead bought F-16 Fighting Falcons. Despite the financial constraints, several minor upgrades were made to allow South Korean F-4s to continue in their role against North Korea. Some F-4s were upgraded with the AN/AVQ-26 Pave Tack laser targeting pod. 30 F-4Es were equipped with the AGM-142 "Popeye" stand-off air-to-surface missile; a modern Israeli weapon also purchased by the USAF, Royal Australian Air Force and the Turkish Air Force. Units Republic of Korea Air Force 10th Tactical Fighter Wing 39th TRG 131st TRS 11th Tactical Fighter Wing 110th TFS 151st TFS 17th Tactical Fighter Wing 152nd TFS 153rd TFS Spain Through the Mutual Defense Aid Program (MDAP), Spain acquired 36 ex-USAF F-4Cs for the Ejército del Aire (Spanish Air Force). These were the only "C" models ever exported, even as second-hand examples.