Here's one discussion in the book, clearly describing impellers in a tunnel. https://archive.org/details/huntforredoctobe0000clan_l6h7/page/56/mode/2up?q=tunnel

Here's one discussion in the book, clearly describing impellers in a tunnel. https://archive.org/details/huntforredoctobe0000clan_l6h7/page/56/mode/2up?q=tunnel https://archive.org/details/huntforredoctobe0000clan_l6h7/pa... For example, it says the US "looked at this back in the early sixties and got to the model stage before dropping it. One of the things they discovered is that one impeller doesn’t work as well as several. Some sort of back pressure thing." Wikipedia says, at https://en.wikipedia.org/wiki/The_Hunt_for_Red_October https://en.wikipedia.org/wiki/The_Hunt_for_Red_October : > The movie is a nearly faithful depiction of the novel even though there are many deviations, including Red October traveling up the Penobscot River in Maine to dry dock, the omission of the Royal Navy task force including Ryan's time aboard HMS Invincible, and the "caterpillar drive" being described as a magnetohydrodynamic drive system, essentially, "a jet engine for the water", rather than a drive powered by a series of mechanical impellers inside flow tunnels.