Pumping tests furnished data for calculation of coefficients of storage and transmissibility at three army camps in Mississippi but water-level declines depend also on correct analysis of the geology of Tertiary sediments involved.The water supply for Camp McCain comes from an upper sand of basal Claiborne age and a lower sand of middle Wilcox age. The productive basal sand of Claiborne age has a large catchment area in its nearby outcrop, where it overlaps the sand of middle Wilcox age. The lower of these two sands is a nearly discontinuous deposit in three east-west tortuous ancient channels truncated near the middle of the camp by a north-south reverse fault. The cones of depression in it are extensive and irregular and the coefficients of transmissibility and storage range widely. It yields less water than the upper sand but its water is of better quality, and has therefore been developed to economic maximum.The Camp Van Dorn water supply comes from four aquifers within a Miocene deltaic mass. Most wells are in a sand at the base of the Homochitto member of the Pascagoula formation, which crops out 15 miles up-gradient and north of the camp. Large undeveloped supplies remain.The water levels at Camp Shelby declined for six months and then remained nearly stationary for more than a year. No outcrops of the water-bearing sand of Miocene age could be found, but recharge occurs from the Pleistocene gravels in nearby river valleys.This paper is based on ground-water investigations made in cooperation with the Mississippi State Geological Survey.