  The history and advances of neutronics calculations at Los Alamos during the
Manhattan Project through the present is reviewed. We briefly summarize early
simpler, and more approximate neutronics methods. We then motivate the need to
better predict neutronics behavior through consideration of theoretical
equations, models and algorithms, experimental measurements, and available
computing capabilities and their limitations. These, coupled with increasing
post-war defense needs, and the invention of electronic computing led to the
creation of Monte Carlo neutronics transport. As a part of the history, we note
the crucial role that the scientific comradery between the great Los Alamos
scientists played in the process. We focus heavily on these early developments
and the subsequent successes of Monte Carlo and its applications to problems of
national defense at Los Alamos. We cover the early methods, algorithms, and
computers, electronic and women pioneers, that enabled Monte Carlo to spread to
all areas of science.
