Earlier: https://news.ycombinator.com/item?id=46279611

The Physics of Explosions underwater: Key Phenomena of Underwater Explosions

    Shock Wave Propagation:

        In Air: The shock wave dissipates much more quickly.

        Result: The water's high density and incompressibility allow the shock wave's energy to be transmitted more efficiently and for a longer duration to targets.

    The Gas Bubble (Cavitation):

        After the initial detonation, the gaseous products of the explosion form an extremely hot, high-pressure bubble.

        Unlike in air, this bubble rapidly expands, then contracts due to the external pressure of the water (which is much greater than atmospheric pressure). This cycle of expansion and contraction, called oscillation, can repeat several times.

        During contraction, the bubble collapses violently, creating a second, less intense, but still powerful pressure pulse.

        If the bubble collapses near a solid surface (like a ship hull), it can generate a high-speed jet of water, known as the "water hammer" or "bubble pulse", which causes significant localized damage. This phenomenon is unique to underwater explosions and contributes greatly to the total damage.

    Hydrostatic Pressure:

        The ambient hydrostatic pressure (the pressure exerted by the water depth) is higher than atmospheric pressure, which influences the gas bubble's dynamics, causing it to collapse faster and more violently than it would in air.

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