Radio direction finding was used extensively throughout the wars in Southeast Asia in an attempt to pinpoint the location of enemy radios and to gain real-time intelligence from listening in to the transmissions. The first attempt to provide an RDF capability came in March 1962 when a modified C-54 was deployed to Tan Son Nhut under the project name Hilo Hattie. This was not successful and was soon withdrawn but in February 1964 a modified C-47, under the project name Hawkeye, was sent to Vietnam for a six-month trial. The aircraft returned to Vietnam the following year and flew a number of successful missions. The entire RDF effort was at that time organised by the US Army whose 3rd Radio Research Unit operated modified U-6 Beavers in the role. However, the USAF wanted to take over the role and set about converting additional C-47s with a much better capability than the original aircraft or the Army U-6s. Project Phyllis Ann eventually resulted in a total of 57 C-47s converted to the RDF role for use in Southeast Asia. The first aircraft arrived on 26 May 1966 to join the 360th TRS, which had been activated at Tan Son Nhut on 8 April. Two more squadrons were activated, the 361st at Nha Trang and the 362nd at Pleiku. The 6994th Security Squadron was activated on 15 April and all the security and communications specialists on board the aircraft belonged to this unit. In the last six months of 1966 the RDF RC-47s flew a total of 1,146 missions, mostly in South Vietnam, but some over Laos where intelligence on the Ho Chi Minh Trail was particularly valuable. In an attempt to disguise the highly-classified nature of the aircraft, a leaflet chute was built into one of the RC-47’s windows so that the aircraft could pose as leaflet droppers. By early 1968 the aircraft had been redesignated as the EC-47.