Braniff International Airways would be the only customer for the Series 200 of the Boeing 707 jetliner. While the original 707 production version was designated the 707-120, Braniff's aircraft were 707-200s (actually 707-227s using Braniff's customer number). The -120 used the JT3C turbojet which provided 13,200 lbs of thrust and was the civilian version of the military J57 engine. The -227, on the other hand, used the more powerful JT4A engine with 15,800 lbs of thrust and was the civilian version of the J75 engine that was used on the F-105 Thunderchief, F-106 Delta Dart and the U-2. The JT4A (which was also used on the Douglas DC-8-20) gave Braniff plenty of extra power at some of the hot-and-high airports of the US Southwest and Latin America and did not require water injection for a takeoff boost.
Only five 707-227s were built- the first one was lost on a pre-delivery test flight on 19 October 1959. The remaining four were flown by Braniff until 1971 when they were traded to BWIA (British West Indies Airlines).
Source: Airways, October 2009. "Braniff's 'El Dorado Super Jet' 707s" by Ed Davies, p41, 44.