In 1954 Rolls-Royce introduced the first commercial bypass engine, the Rolls-Royce Conway, with 17,500 lbf (78 kN) of thrust aimed at what was then the "large end" of the market. This was far too large for smaller aircraft such as the Sud Caravelle, BAC One-Eleven or Hawker Siddeley Trident which were then under design. Rolls-Royce then started work on a smaller engine otherwise identical in design derived from the larger RB.140/141 Medway - which itself had been cancelled after British European Airways (BEA) had demanded the downsizing of the Trident, the RB.163, using the same two-spool compressor arrangement and a smaller fan delivering bypass ratios of about 0.64:1. Designed by a team under Frederick Morley, the first versions of what had become the 'Spey' entered service in 1964, powering both the 1-11 and Trident. Several versions with higher power ratings were delivered through the 1960s, but development was ended nearing the 1970s due to the introduction of engines with much higher bypass ratios, and thus better fuel economy.