It was a window in the non-watertight entrance tunnel, not the window in the hull. This article describes it in more detail: https://spectrum.ieee.org/amp/don-

It was a window in the non-watertight entrance tunnel, not the window in the hull. This article describes it in more detail: https://spectrum.ieee.org/amp/don-walsh-describes-the-trip-to-the-bottom-of-the-mariana-trench-2650257923 https://spectrum.ieee.org/amp/don-walsh-describes-the-trip-t...