The engines about which this paper is written are called "Liberty." They came in series of 4, 6, 8, and 12 cylinders and were developed for interchangeability of parts and ease of production.

Foreword -- Preface -- Ante bellum -- Missions and commissions -- Birth of a concept -- To design an engine -- The engines -- Ground tests -- Flight tests -- The critics -- Organization for production -- The producers-- The liberty goes to war -- Post bellum -- Appendix -- Bibliography.