NavList:

The next big spectacle in the popcorn stadium, opening in just two days, is sure to draw questions from sailors and ocean navigation pundits everywhere. It's Tom Cruise and Hayley Atwell and Ving Rhames and Simon Pegg and Rebecca Ferguson starring in Mission: Impossible – Dead Reckoning Part One. Here's a review talking up the crazy stunts, and a crazy trailer teasing us with the crazy stunts.

My prediction: somewhere on the internet folks will start blathering about the origin of the term "dead reckoning" and some subset of that group will assert their expertise and inform us that, "You know, it's really supposed to be Ded Reckoning, not Dead". They're dead-wrong.

First things first, like a lot of very old seafaring terminology, the exact original sense of the phrase, its etymology and origin, are lost to history. We know what the term has meant in navigation for the past few centuries, and we know that the word "dead" is not uncommon in the nautical world, usually reserved for something motionless.

The meaning of dead reckoning, distinct from its lost etymology, is clear enough. It is the mathematical, sometimes graphical procedure of adding up the "vectors" of a vessel's course and speed over some extended period of time in order to determine how far it has travelled, where it is now, after various steps of motion of known lengths in known directions. In modern navigation, starting in the 20th century apparently, it became popular to suggest that the uncertainties of "dead reckoning" brought about by unknown errors in course and speed, whether due to imperfect measurement or caused by currents and winds could be life-threatening. In pithy terms, "dead reckoning" will make you "dead".

Unfortunately, just about a century ago, a false or "folk etymology" --or, as I have dubbed it, an ety-mythology-- took hold thanks to one little letter to the editor. The author was Henry Harries, a marine meteorologist, and his letter was apparently published in the "London Morning Post" (I haven't see the original, so this attribution is from secondary sources). The claim was that "dead" and "ded" were alternate spellings in an era when spelling in the English language was more fluid. The claim then insists that the original was probably "ded reckoning". And then, now in full-on speculative mode, the claim continues that "ded" was short for "deduced". That is the "dead reckoning" was the "reckoning" of a vessel's position as "deduced" from a record of its course and speed over a period of time. This is a classic "just-so" story, a tale that satisfies our need for an explanation, but it's a story that has scarcely any basis in historical evidence or fact.

Why did the folk etymology succeed? Quite possibly, though here I am speculating, too, air navigators, who had just begun using the navigation methods of seagoing mariners, saw the expression dead reckoning as improbable and weird. There was little use for the word "dead" in the aviation world except at the end of a stall and a crash. Aviators needed a "just-so" story, and that story from the newspaper letter got legs and began to run. Following the aviators decades later, the world of robotics has given the folk etymology mechanical legs, and almost any introduction to the basics of automated navigation in robots will lead off with a confidently re-told tale explaining that "dead reckoning is 'really' ded reckoning". As I have said it's a tall tale. This was one man's attempt to fill in a hole eagerly welcomed by folks who didn't like the hole. That's how folk etymologies thrive... one speculative story at a time.

Why does the new film in the very successful "Mission Impossible" series need the phrase "Dead Reckoning"? I doubt there's even a passing connection to navigation. Most likely someone simply liked the ominous ring of it. That's probably the same reason for other movies and pop culture products named for Dead Reckoning in the past century. It just sounds so intriguing!

Frank Reed
Clockwork Mapping / ReedNavigation.com
Conanicut Island USA

Another night at the movies... A movie with "Dead Reckoning" in the title, even though it's probably only used for its ominous tone, will be worth some conversation, but if that's not enough entertainment, we are today only eleven days from the movie spectacle now known as Barbenheimer --the unholy double-feature mashup of the "Barbie" movie, which is about the doll, Barbie, coming to life, sort of (here's a trailer with a lunar in it, yes, really, sort of) played against the story of J. Robert Oppenheimer's life in and out of the Manhattan Project. Often known as "Oppie" in his day, which also aligns nicely with "Barbie", his most famous contribution to pop culture was probably his quotation from the Bhagavad-Gita after seeing the Trinity test of the atomic bomb. See the doll... Stay for the mushroom cloud.