An experimental evaluation of the transmission of shock waves from a detonating gas mixture in a 0.5-in-inner-diameter open-ended tube into an inert atmosphere is described in this paper. Stoichiometric H 2 /O 2 at 1 atm was used as the reactive gas medium. Results from in-tube diagnostics indicated successful deflagration-to-detonation transition (DDT), which leads to an overdriven detonation before exiting the tube at near Chapman–Jouguet (CJ) conditions. Out-of-tube diagnostics characterized the transmission of the shock wave into the surrounding environment, where the shock wave decays into an acoustic wave as it travels away from the tube exit. A mathematical treatment of overpressure and time-of-arrival data allowed for a direct analytical description of the transmitted shock wave’s transient velocity. This description is combined with a first-principles gas-dynamics treatment of the moving normal shock wave to describe the conditions behind the attenuating shock wave. This work furthers the understanding of shock transmission from an open-ended detonation tube and provides a theoretical framework to estimate the resulting conditions.