By the mid 1950's with the advent of relatively thin, flexible aircraft wings, a new and dangerous phenomenon related to aircraft elasticity was being encountered. Many pilots were experiencing flutter, or severe buffeting and oscillations during flight. The needs to understand this new phenomenon lead to the development of the TDT or Transonic Dynamics Wind Tunnel at NASA Langley. This new tunnel not only tested the elastic properties of aircraft, but also a host of other aerodynamic situations in an effort to save lives.

Additional Information
http://www.airspacemag.com/asm/mag/supp/fm01/Hammer.html