Introduction of the Large Proposal category for HST observing in Cycle 11 resulted in a significant migration toward multiple observing programs requiring 100 or more orbits on single target areas. While relatively benign in the inaugural Cycle, this policy created a formidable planning problem in Cycle 12 due to acceptance of several large programs with identical or closely located targets. The nature of this observing pool revealed shortcomings in the established processes for building an integrated HST science plan. Historically it has not been difficult to normalize individual programs within the overall HST observing plan. However, conflicts arising from competing demands and overlapping time windows in Cycle 12 necessitated compromises between programs at a more significant scale than experienced ever before. The planning tools and techniques needed to change rapidly in response, and communication both within the STScI and between the STScI and the affected observers was more crucial than ever before. Large and small-scale changes to major observing programs were necessary to create a viable integrated observing plan. This paper describes the major features of the Cycle 12 observing pool, the impact it had on the STScI front-end operations processes and how an executable Cycle 12 HST observing program was achieved.