The slow magnetic dynamics, from seconds to kiloseconds, of the canonical 3-k antiferromagnet USb have been probed, using X-ray photon correlation spectroscopy (XPCS). In this work, XPCS is combined with resonant X-ray diraction to focus on scattering at an antiferromagnetic Bragg peak. High quality coherent magnetic diraction patterns were recorded (speckle contrast of 88%) and magnetic domains were observed; the number of domains increases on warming to T 160 K, where the spin waves soften to zero frequency, and again on warming to TN = 218 K. The intensity auto-correlation, g2(t), is primarily static over 1000 s, with a small dynamical process (change of 0:4%) that increases in rate close to the transitions. ; JRC.E.6-Actinide research