The use of UC-123 Providers in Ranch Hand defoliation operations was becoming increasingly dangerous, especially in high-threat areas such as the Ho Chi Minh Trail in southern Laos. In an effort to increase survivability the use of fast jets as spray aircraft was proposed and experiments were conducted in the field. It was thought that the use of fast jets would not require escort or suppression aircraft to accompany the spray aircraft as was necessary with the Providers. The 390th TFS was chosen to perform trials and at least three of the Squadron’s F-4Ds were fitted with modified underwing tanks fitted with spray nozzles. The first spray test mission took place over Da Nang on 17 January 1969 and the first of only seven combat spray missions was flown on 25 January. The missions involved three spray aircraft flying in a V-formation at 500 knots and 100-200 feet above the jungle. The area to be sprayed was marked by a FAC and a 10-mile swath some 300 feet wide could be sprayed in 70 seconds. Several tank failures occurred and when an aircraft was shot down on 29 March the programme was terminated. Attempts to revive the fast jet spray project later in the year eventually came to nought. All Ranch Hand defoliation operations in Southeast Asia came to an end on 9 May 1970 after which the C-123-equipped 12th SOS devoted its efforts to psychological warfare and flare dropping missions in support of the Cambodian incursion.