The first comprehensive analysis code (C81) is developed

Description

"The complexity and multidisciplinary nature of rotorcraft aeromechanics problems demands a software tool called a comprehensive analysis: applicable to a wide range of problems (performance, loads, vibration, response, stability) and operating conditions (hover, cruise, maneuver), and a wide class of configurations (blades, hubs, rotors, aircraft), in all stages (research, conceptual design, detailed design, development) and all aspects (design, testing, evaluation) of the engineering process."

Source: "Milestones in Rotorcraft Aeromechanics", Johnson W., , NASA/TP-2011-25971, May 2011, Page 44)

The first such code was C81, developed by Bell Helicopter (supported by the US Army). This milestone is represented by the publishing of the a paper in the AHS Journal  by the developers of C81. The reference is provided below,

Blankenship, B. L., and Harvey, K. W.: A Digital Analysis for Helicopter Performance and Rotor Blade Bending Moments. Journal of the American Helicopter Society, vol. 7, no. 4, Oct. 1962, pp. 55–69

Note: Only the month and year of this milestone are known - March 31 has been chosen as an approximate but conservate date