The analysis of the numerical study of underwater high-speed gas jets is presented in this study. This work aims to understand the development of the flow structure of the gas jets submerged in water and assess the performance of the jet in terms of the thrust under varying operating conditions. The behavior of the submerged gas jet is studied under two operating parameters, namely, the pressure ratio (ratio of the pressure of the gas jet at the nozzle exit to ambient pressure) and the depth of water at which the propulsion takes place. The effort utilizes computational fluid dynamics using the finite volume method to solve the unsteady Reynolds-averaged Navier–Stokes equations in a two-dimensional axisymmetric domain combined with the mixture model for the multiphase flow. The unsteady behavior of different flow variables under varying operating parameters is discussed in detail. Further, the flow physics of a submerged supersonic gas jet is compared with a supersonic gas jet expanded in the air under a similar set of operating parameters. The effects of density difference between the gas and water have been studied from the comparative analysis. Copyright © 2022 by ASME.