A low-speed wind-tunnel investigation of a slender body of square cross-section was conducted to determine the effect of boattail geometry on the base pressure coefficient. The data were obtained over an angle-of-attack range of 0 to 8 degrees. Surface flow patterns were visualized using tufts. An exploratory numerical modeling effort was also performed. The base pressure showed the expected decrease from top to bottom as the body angle of attack was raised. The base pressure coefficient showed a rapid rise when the angle of attack increased past 4 deg.