Submerged massive gas injection into liquid is a process intensification method that enhances the reaction rates through better stirring and mixing. Particularly, in metallurgical processes such as argon-oxygen decarburization (AOD) converter, high-speed injection of gas into molten metal facilitates the reduction of dissolved carbon. The gas injection velocity in such applications could reach the speed of sound and in several cases even constitute a supersonic gas flow penetrating high-density liquid. Such extreme conditions usually involve various sources of physical complexity such as gas compressibility, instabilities at the liquid-gas interface, and shock dynamics that eventually determine different flow regimes. This study presents a small-scale interface-resolved LES simulation of air-to-water injection at the near-nozzle region pursuing a validation strategy with water-based experiments. Using the compressible volume of fluid (VOF) method, we have simulated submerged massive gas injection into the water at different injection pressures. The simulations show reasonable agreement with macroscopic quantities obtained from flow measurement and high-speed imaging e.g. the mass flow rate and Mach numbers. We identified different regimes during gas penetration: at lower injection pressures, the flow becomes slightly supersonic with oscillatory shock wave structure inferring a bubbling regime, and as the pressure increases the flow encounters higher Mach numbers with stronger shocks establishing a more stable jetting regime. The total interfacial area, that is an indicator of gas fragmentation, increases with the injection pressure. This could be attributed to the Richtmyer-Meshkov instability during the shock-interface interactions. We also observed in both experiment and simulation that the probability of back-attack phenomenon decreases with the injection pressure which is consistent with the previous findings in existing literature. This may be explained by the dynamics of traveling shocks, their reflection at the liquid-gas interface, and their interference inside the compressible gas core. Due to the limitation of the optical measurement techniques in this context, this highly-resolved simulation study offers a basis for the physical interpretation of compressibility effects during massive gas injection in metallurgical plants.