The Brennan torpedo, invented in 1877 by Louis Brennan, was one of the first (if not the first) guided torpedoes of a practical design. Amazingly, it had no internal power source but it did have a very clever and counter-intuitive mode of operation: a cable was pulled backward to propel the torpedo forward.

If the idea of sending something forward by pulling a cable backward seems unusual, you’re not alone. How can something go forward faster than it’s being pulled backward? That’s what led [Steve Mould] to examine the whole concept in more detail in a video in a collaboration with [Derek Muller] of Veritasium, who highlights some ways in which the physics can be non-intuitive, just as with a craft that successfully sails downwind faster than the wind.

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