The following year, American Airlines revised its requirement to a four-engine design for 75 passengers with range. Lockheed proposed a new design, the CL-310 with a low wing and four Rolls-Royce Darts or Napier Elands. The CL-310 design met the American Airlines requirements, but failed to meet those of another interested carrier, Eastern Air Lines. Its requirements were for a longer range; a minimum cruising speed of ; and increased seating capacity to the 85-to-90-passenger level. Lockheed redesigned the CL-310 to use the Allison 501-D13, a civilian version of the T56 developed for the Lockheed C-130 Hercules military transport. The airframe was stretched to allow for more seats and handle the increased performance. This design was launched as the Model 188 with an order for 35 by American Airlines on June 8, 1955. This was followed by Eastern Air Lines with an order for 40 on September 27, 1955. The first aircraft took 26 months to complete and by that time Lockheed had orders for 129. The prototype, a Model 188A, first flew on December 6, 1957, two months ahead of schedule. Lockheed was awarded a type certificate by the Civil Aeronautics Administration (CAA) on 22 August 1958. The first delivery – to Eastern Air Lines – was on October 8, 1958, but it did not enter service until January 12, 1959.