  A rapidity gap program with great potential can be realized at the Large
Hadron Collider, LHC, by adding a few simple forward shower counters (FSCs)
along the beam line on both sides of the main central detectors, such as CMS.
Measurements of single diffractive cross sections down to the lowest masses can
be made with an efficient level-1 trigger. Exceptionally, the detectors also
make feasible the study of Central Diffractive Excitation, and in particular
the reaction g + g to g + g, in the color singlet channel, effectively using
the LHC as a gluon-gluon collider.
