  We outline a physics program at Fermilab that would significantly improve our
ability to understand the behavior of hadronic showers in calorimeters. This
would involve a two-pronged approach designed to measure particle production
cross sections of hadronic beams on several nuclei to improve shower simulation
programs and the validation of the improved shower simulation predictions using
test beams (including tagged neutral beams) in which calorimeter modules built
using various technologies are deployed in the test beam. Such a program would
be of immediate benefit to the efforts to design and build optimal calorimeters
for the International Linear Collider.
