Experimental studies are carried out on an axisymmetric cylindrical base body for six freestream Mach numbers between 0.54 and 1.41. Unsteady pressure is measured on the base surface using high-frequency response Kulite pressure transducers. The effect of passive flow control devices on the mean base pressure and the unsteady characteristics of base pressure have been studied. A blunt base, a conventional cavity device, and three different ventilated cavity devices have been tested along with four different rounded base lip devices. A total of 20 different base geometric modifications are tested at 6 freestream Mach numbers resulting in 120 test cases. The cavity devices improve the base pressure as compared to the blunt base case, particularly for freestream Mach numbers more than 0.98. Among all the cases considered, a maximum increase of 8.6% in the base pressure coefficient is noticed for the normal ventilated cavity device as compared to the blunt base case for freestream Mach number of 1.22. The power spectral density of base pressure fluctuations revealed the dominant peaks on the base surface. The Strouhal number associated with the coherent structures developing in the shear layer varies between 0.2 and 0.27 for the six freestream Mach numbers considered. In the presence of cavity devices, dominant peaks are observed for Strouhal numbers between 1 and 5. The root-mean-square, skewness, kurtosis of the base pressure fluctuations for all the cases are presented. Maximum reduction in base pressure fluctuation is observed for the normal and inclined ventilated cavity device configuration test cases.