Some old and hard-to-find papers

• Bray, Crawford, and Proschan (1967)
  
  Maximum likelihood estimation of a U-shaped failure rate function.
  Mathematical Note 534, Mathematics Research Laboratory, Boeing Scientific Research Laboratories,
  Seattle, Washington
   
• Saunders (1975)
  
  Birnbaum's Contributions to Reliability Theory.
  In Reliability and Fault Tree Analysis;
  Theoretical and Applied Aspects of System Reliability and Safety Assessment.
  SIAM, Philadelphia, 1975. pages xv-xxxix.


• Crawford Saunders (1963)
  
  Non-Parametric Maximum Likelihood Estimation
  Boeing Scientific Research Laboratories, October 1963.
  


• Crawford (1967)
  
  Maximum Likelihood Estimation: A Practical Theorem on Consistency of the
  Nonparametric Maximum Likelihood Estimates with Applications
  Boeing Scientific Research Laboratories, February 1967.
  


• Bray Crawford Proschan (1967)
  
  Maximum Likelihood Estimation of a U-Shaped Failure Rate Function
  Boeing Scientific Research Laboratories, October 1967.