Wind-tunnel work on the Electra was undertaken at the University of Michigan. Much of the work was performed by a student assistant, Clarence Johnson. He suggested two changes be made to the design: changing the single tail to double tails (later a Lockheed trademark), and deleting oversized wing fillets. Both of these suggestions were incorporated into production aircraft. Upon receiving his master's degree, Johnson joined Lockheed as a regular employee, ultimately leading the Skunk Works in developing advanced aircraft such as the Lockheed SR-71 Blackbird.