What's Up With "10-4" And Other Radio Lingo?

comstock/Stockbyte via Getty Images
comstock/Stockbyte via Getty Images


Reader and frequent question-asker Nate J. wrote in wondering why we say things like "10-4" and "Roger" on walkie-talkies and other two-way radios.

The Ten-Codes

The ten-codes or ten-signals are code words used as stand-ins for common phrases in radio communication. Charles Hopper, a communications director with the Illinois State Police, developed them in 1937 to combat the problem of the first syllables or words of a transmission being cut off or misunderstood. Preceding every code with "ten" gave the sometimes slow equipment time to warm up and improved the likelihood that a listener would understand the important part of a message. The codes also allowed for brevity and standardization in radio message traffic.

The codes were expanded by the Association of Public-Safety Communications Officials-International (APCO) in 1974 and were used by both law enforcement agencies and civilian CB radio users. Over time, differing meanings for the codes came about in different agencies and jurisdictions, undoing the codes' usefulness as a concise and standardized system. The problem came to a head in 2005 during rescue operations after Hurricane Katrina. After several instances of inter-agency communication problems, the United States Federal Emergency Management Agency (FEMA) discouraged the use of ten-codes and today the federal government recommends they be replaced with plain, everyday language. Here's the official APCO list.

Roger That

In the days of the telegraph, the Morse code letter R (dot-dash-dot) was sometimes used to indicate "received" or "message received/understood." When radio voice communication began to replace telegraphs, Roger, the code word assigned to the letter R in the Joint Army/Navy Phonetic Alphabet (the radio alphabet used by all branches of the United States military from 1941 to 1956), took on the same role.

Contrary to what Hollywood would have you think, Roger only means "last transmission received/understood" and does not also mean or imply "I will comply." Wilco (Will Comply) is the code used if the speaker intends to convey "message received and will comply." Given that, the phrase Roger Wilco, which you so often hear in the movies, is redundant and not really used since Wilco alone covers all the bases and acknowledges receipt of message and states intent to comply.

Mayday

Mayday is an international code word used to signal life-threatening emergencies. It was originated in 1923 by Frederick Stanley Mockford, a senior radio officer at London's Croydon Airport. He was given the task of coming up with a unique and easily understandable emergency code word. Most of the air traffic at Croydon was either coming from or going to Le Bourget Airport in Paris, so Mockford chose mayday because of its similarity to the French m'aider ("come help me").

Because it is an emergency signal, there are plenty of rules governing the use and format of a mayday call. A mayday call can only be made when life or craft is in imminent danger of death or destruction (and, as with fake 9-1-1 calls, fake mayday calls are considered serious crimes. In the U.S., making a fake distress call is a federal crime that can carry large fines and jail time), and once one is made, no other messages can be transmitted except to assist in the emergency.

Correct format for a Mayday call is:

- "Mayday, Mayday, Mayday." The call is always given three times in a row to keep it from being mistaken for a similar-sounding phrase, or to distinguish an actual distress signal from a message about a mayday call.

- "This is ____." The vessel name is repeated three times, followed by call sign if available.

- "Mayday. [vessel name]."

- "My position is ____." Position is given in latitude-longitude coordinates, or bearing and distance from a fixed point.

- "I am _____." The type of emergency, e.g. fire or sinking.

- "I require immediate assistance."

- "I have _____." The number of people on board and their condition, as well as any other pertinent information, e.g. abandoning to life rafts.

- "Over."

Some radio instructors suggest the mnemonic MIPDANIO for learning mayday signal format: Mayday, Identify, Position, Distress, Assistance, Number of crew, Information, Over.

Phonetic or Spelling Alphabets

The problem: a lot of letters sound alike. If two people are talking to each other on the telephone or a two-way radio, an "N" might be misheard as an "M," or a "B" might be heard as a "D," "T," or "C." If one person tells the other that the secret code that must be entered to save the world from imminent disaster is "M-A-T-T", there's a chance that we might all die because a little bit of static could cause the code to be heard as "N-8-B-D."

The solution: a phonetic alphabet or spelling alphabet, where code words are assigned to the letters of the alphabet acrophonically (that is, the code word assigned to a given letter starts with that letter, like Alpha for "A"). Using the Joint Army/Navy Phonetic Alphabet mentioned earlier, the above code becomes "Mike-Able-Tare-Tare" which is a little harder to mishear.

Today, the most commonly used spelling alphabet is the International Radiotelephony Spelling Alphabet. The alphabet was developed by the International Air Transport Association (IATA) and International Civil Aviation Organization (ICAO) after World War II and later adopted by organizations like International Maritime Organization (IMO), the Federal Aviation Administration (FAA), the American Radio Relay League (ARRL), and the North Atlantic Treaty Organization (NATO) (whose use of the alphabet led to its global spread and use of the common name, NATO phonetic alphabet).

In addition to these (and other) organizations, the alphabet is used by the military and in civilian industries (retail, IT and airlines for instance). The alphabet in its current form is:
Alfa
Bravo
Charlie
Delta
Echo
Foxtrot
Golf
Hotel
India
Juliet
Kilo
Lima
Mike
November
Oscar
Papa
Quebec
Romeo
Sierra
Tango
Uniform
Victor
Whiskey
X-ray
Yankee
Zulu.

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Why Do We Celebrate Christmas on December 25?

If Jesus wasn't born on December 25, does this rule still apply?
If Jesus wasn't born on December 25, does this rule still apply?
Jon Tyson, Unsplash

Each December, Christians throw a collective birthday bash to celebrate the anniversary of Jesus’s arrival on Earth. But without a birth certificate—or any other official record of his actual birthdate—in existence, December 25 seems like an arbitrary day for all our Christmas traditions. So how did early observers choose it?

When Was Jesus Really Born?

Since the Bible doesn’t name a month or even a season for Jesus’s birth, historians have relied on other context clues to estimate when it occurred. Shepherds tend sheep in the Nativity story, which people often cite as evidence that Jesus was more likely born during the spring. Others argue that Israel’s mild winter temperatures allow sheep to graze even in December. According to Slate, it’s also possible that sheep set aside for religious sacrifices may have been given free rein, frigid night or not.

The Adoration of the Shepherds by Sebastiano Conca, 1720.J. Paul Getty Museum // Public Domain

One clue pointing specifically to December 25 comes from the story of Mary’s cousin Elizabeth, who approached old age without having given birth to any children. One day, her husband, a priest named Zacharias, was burning incense in the temple when the angel Gabriel appeared to him with good news: Elizabeth would bear a son. Early Christians guessed that Zacharias was probably in the temple for Yom Kippur, which they believed always took place on September 24 (it actually shifts year to year based on the Jewish lunisolar calendar). Nine months after September 24 is June 24, so they chose that as the birthdate—and feast day—of Elizabeth and Zacharias’s son, John the Baptist. When Gabriel later visited Mary to let her know that she’d bear a son, too, he mentioned that Elizabeth was in her sixth month of pregnancy. That means Jesus would’ve been conceived in late March, and born in late December—the night of December 24, to be exact, or the early hours of December 25.

Another theory suggests that Christians arrived at December 25 based on an ancient Jewish idea that prophets die on their birthday. During the 3rd century CE, theologists like Tertullian and Hippolytus dated Jesus’s crucifixion to March 25, since it happened around Passover. But to Sextus Julius Africanus, it was less about when Jesus was born and more about when he first came to Earth; in other words, he believed Jesus’s death and conception coincided on March 25, and thus his birth occurred on December 25 [PDF].

The Early History of Christmas

Even if Zacharias was in the temple on September 24, Gabriel did visit Mary exactly six months later, and Jesus was born right on his due date, it’s still possible that we celebrate Christmas on December 25 for a different reason altogether.

While 3rd-century Christians were busy worshiping the Son of God, some of their pagan counterparts were busy worshiping the Sun God. In the 270s, Roman emperor Aurelian popularized the cult of Sol Invictus, or “The Unconquered Sun,” whose feast day was celebrated on December 25. According to John Carroll University history professor Joseph F. Kelly, other Romans revered a Persian god, Mithra, whose feast day also may have fallen on December 25. There was also Saturnalia, an annual Roman festival that ran from December 17 to December 23. In short, many ancient Romans were well-accustomed to celebrating something in late December by the time Christianity entered the mainstream.

A painting of Saturnalia festivities by Antoine Callet, 1783.Themadchopper, Wikimedia Commons // Public Domain

That happened during Constantine’s rule over Rome in the early 4th century. In 313, Constantine and his fellow ruler Licinius issued the Edict of Milan, which basically legalized Christianity and condemned the ongoing persecution of anyone who practiced it. Constantine was a devout Christian himself, and he spent the rest of his reign spreading the religion throughout the empire. The first known record of December 25 as Jesus’s official birthday is from 336, the year before Constantine died. Because it’s mentioned in a volume containing other important religious dates, some have assumed that a celebration probably occurred on that day, and 336 is often cited as the first known “Christmas.”

Whether Christians celebrated Christmas on December 25 before 336 may forever be unknown, but we do know that the custom quickly caught on (spending the holiday watching A Christmas Story marathon wouldn't come until much later). By the end of the 4th century, Christian bishops were holding Christmas Mass all over Rome, and pagan festivals soon fell out of fashion. The fact that Christmas essentially replaced those earlier December traditions could be a coincidence, but some believe it was by design: Since Romans were already primed for parties on December 25, the Church could’ve been trying to co-opt a built-in subscriber base.

In summary, the origins of Christmas are just as subject to interpretation as Jesus’s actual birthdate—so feel free to play Christmas music whenever you want.

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