If the competition for the trijet market had been stiff, that for the twinjets was intense, and there were three contenders, not two. Once again the British had made the early running, with the British Aircraft Corporation's BAC One-Eleven, which went into service with Braniff on 25 April 1965. Like the Caravelle, the Trident and the Boeing 727, the One-Eleven's engines were mounted on the rear of the fuselage. But by the time of its first service, Douglas had produced a similar aircraft, the DC-9, which, in its first version, the DC-9-10, had first flown on 25 February of the same year.
The Douglas company outsold B.A.C. very quickly because, true to Douglas tradition, it developed the basic type almost as soon as the first blueprints were signed off. Indeed, the DC-9-30, the most popular of the line, was into service on 1 February 1967, with Delta, before Boeing got into the twin-jet act.
Going against the apparent tide of design trends, Boeing decided to mount the 737 engines on the wing. This was partly because it had taken the decision to make yet another permutation of the possibilities of the successful 727 fuselage and by shortening it, had compromised engine location. However, although the stubby shape led to ribald remarks from the aesthetically-minded, and the low-slung engines drew serious reservations from the technical critics, Boeing perservered.
The 737-100 first flew on 9 April 1967 and went into service with the German airline Lufthansa, and was not a marketing success. But Boeing soon followed this up with the 737-200, which, although slow in the early years, became a big winner. United was the first operator, starting service on 28 April 1968, and slowly but surely, Boeing began to steal the markets away from Douglas and B.A.C., which by now was a poor third in the running. Once again, Boeing was ready to comply with special customer wishes, producing its now well-known gravel kit to enable the 737, even with its low-slung engines, to be able to use strips that the rear-engined rivals could not.