Velocimetry measurements have been established inside of a 6.06” (~154 mm) radially fed Rotating Detonation Engine. The engine has a channel gap width of 0.3” (7.62 mm) making the inner diameter 5.46” (~139 mm), and an air gap height of 0.022” (0.56 mm). The fuel plenum consists of 80 discrete injection points that are 0.035” (~.89 mm) in diameter and impinge axially on the radially fed air as to assist in mixing. The oxidizer was air, and the fuel was hydrogen combusted at stoichiometric conditions with a total mass flux of 200 kg/s*m2. Particle Image Velocimetry was utilized to capture the flow field inside of the engine. The area of interest was 1” by 1” with a spatial resolution of 12 μm/px, and an interframe time of 1 μs. It was found that directly behind the transverse detonation wave (within the same axial region) velocity dropped to nearly half of the total wave speed, approximately 900 m/s. However, just above the detonation the velocity magnitudes were on the order of the transverse wave speeds, approximately 1600 m/s. These results were validated against Computational Fluid Dynamics provided by Georgia Tech using the exact same geometry.