ACP 131

ACP-131 is the controlling publication for the listing of Q codes and Z codes. It is published by the Combined Communications Electronics Board (CCEB) countries (Australia, New Zealand, Canada, United Kingdom and United States), and revised from time to time. When the meanings of the codes contained in ACP-131 are translated into various languages, the codes provide a means of communicating between ships of various nations, such as during a NATO exercise, when a common language is not in effect.


The original edition of ACP-131 was published by the U.S. military during the early years of radio telegraphy for use by radio operators using Morse Code on continuous wave (CW) telegraphy. It became especially useful, and even essential, to wireless radio operators on both military and civilian ships at sea before the development of advanced single-sideband telephony in the 1960s.

Reason for the codes

Radio communications, prior to the advent of landlines and satellites as communication paths and relays, was always subject to unpredictable fade outs caused by weather conditions, amount of emission power in kilowatts at the transmitter, radio frequency of the transmission, type of emission, type of transmitting antenna, signal basewave shape and size, sensitivity of the receiver and presence, or lack of presence, of atmospheric reflective layers above the earth, such as the E-layer and F-layers, the type of receiving antenna, the time of day, and numerous other factors.

Because of these factors which often resulted in limiting periods of transmission time on certain frequencies to only several hours a day, or only several minutes, it was found necessary to keep each wireless transmission as short as possible and to still get the message through. This was particularly true of CW radio circuits shared by a number of operators, with some waiting their turn to transmit.

As a result, an operator communicating by CW radio to another operator, wanting to know how the other operator was receiving the signal, could send out a message on his key in Morse Code stating, “How are you receiving me?”


Using ACP-131 codes, the question could be phrased simply “INT QRK”


resulting in much more efficient use of circuit time.

If the receiver hears the sender in a “loud and clear” condition, the response would be "QRK5":


All of which requires less circuit time and less “pounding” on the key by the sending operators.

Should the receiving operator not understand the sending operator, the receiving operator would send “?”


The other operator would respond again with:


which is much easier than retransmitting “How are you receiving me?”

If the receiving operator understood the sending operator, the receiving operator would send "ROGER", or the short form "R"


"R" and "?" are similarly structured, but very easy to distinguish.

Applicability of the codes

According to ACP-125(F), paragraphs 103 and 104, in radio communications involving Allied military units:

  • Q codes are authorized for both civilian and military use, and for communications between the two.
  • Z codes are authorized for use only among military stations.

Applicability of codes by type of emission

  • Civilian radio continuous wave (CW): Q codes.
  • Military radio continuous wave (CW): Q codes and Z codes.
  • Civilian shipboard signal lamp: Q codes.
  • Military shipboard signal lamp: Q codes and Z codes.
  • Military Flag semaphore: Q codes and Z codes.
  • Military teletype: Z codes used as routers in message header.

Voice transmission

Some assert that the use of Q codes and Z codes was not intended for use on voice circuits, where plain language was speedy and easily recognizable, especially when employing the character recognition system in use at the time, such as ALPHA, BRAVO, CHARLIE, etc. However, in military communication the latter are still in use.[1] The latter due to the poor transfer-conditions still suffered on HF band communications (eg, due to heavy swells or Northern Light), ie, for which Q codes and Z codes remain in use. To exemplify the latter, while words such as "received one flash message" may be distorted into unrecognisable clutter, Z codes exhibits a distinctiveness (which enables transfer of radio-messages even under poor conditions).[2]

Typical Simplex military voice exchange:

Q. Lima Five this is Charlie Two – Radio Check Over.
A. Lima Five - roger, over.
A. Charlie Two - roger, out.

However, some voice operators, such as amateur radio operators, find it convenient or traditional to use some of the Q codes, such as QSL, QRK, etc.

See also


  1. ^ Unclassified NATO naval-communication practices/manuals in Northern Europe
  2. ^ Based on the wiki-editors own experience as Naval-Comm-PO

External links

131 (number)

131 (one hundred [and] thirty-one) is the natural number following 130 and preceding 132.

16-line message format

16-line message format, or Basic Message Format, is the standard military radiogram format (in NATO allied nations) for the manner in which a paper message form is transcribed through voice, Morse code, or TTY transmission formats. The overall structure of the message has three parts: HEADING (which can use as many as 10 of the format's 16 lines), TEXT (line 12), and ENDING. This heading is further divided into procedure, preamble, address, and prefix. Each format line contains pre-defined content. An actual message may have fewer than 16 actual lines, or far more than 16, because some lines are skipped in some delivery methods, and a long message may have a TEXT portion that is longer than 16 lines by itself.

This radiotelegraph message format (also "radio teletype message format", "teletypewriter message format", and "radiotelephone message format") and transmission procedures have been documented in numerous military standards, going back to at least World War II-era U.S. Army manuals.

1936 KLM Croydon accident

The 1936 KLM Croydon accident was the crash of a KLM airliner on 9 December 1936, shortly after taking off from the Croydon Air Port (as it was known at the time) on a scheduled flight to Amsterdam, Netherlands. The aircraft was destroyed and 15 of the 17 passengers and crew on board died as a result of the accident.

ACP 125

ACP 125 is the short name for Allied Communications Publication 125: Communications Instructions—Radiotelephone Procedures, developed and published by the Combined Communications Electronics Board, for use by the Five Eyes nations and the rest of NATO. According to the latest version, "The aim of ACP 125 is to prescribe the voice procedure for use by the armed forces of Allied nations on secure and non-secure tactical voice nets. Its purpose is to provide a standardized way of passing speech and data traffic as securely as possible consistent with accuracy, speed and the needs of command and control."The standard defines the procedures for communicating by voice over two-way radio, and has served as the basis for radio communications procedures for many non-military organizations, as well as numerous U.S. government organizations, including the United States Department of State and the Civil Air Patrol.

First published as ACP 125(A) in about 1951, the current version is ACP 125(G), published in 2016. The standard itself is ACP 125, with the letter in parenthesis indicating the major revision level. There are at least two supplements, including:

ACP 125 U.S. SUPP-1: HF Air-Ground Radiotelephone Procedures U.S. Supplement 1 to ACP 125(B)

ACP 125 (US SUPP-2): Radiotelephone Procedures for the Conduct of Artillery and Naval Gunfire (U)

APRS Calling

APRS Calling is a manual procedure for calling stations on the Automatic Packet Reporting System (APRS) to initiate communications on another frequency, or possibly by other means. It is inspired by Digital Selective Calling, a part of the Global Maritime Distress Safety System. It also builds on existing digital procedures inherited from morse code and radioteletype operation. ITU Q codes are used in conjunction with APRS text messages to implement APRS calling. APRS calling is intended to complement monitoring voice calling frequencies.

Allied Communication Procedures

Allied Communication Procedures is the set of manuals and supplements published by the Combined Communications Electronics Board that prescribe the methods and standards to be used while conducting visual, audible, radiotelegraph, and radiotelephone communications within NATO member nations. These procedures relate to procedure words, radiotelephony procedure, Allied Military phonetic spelling alphabets, plain language radio checks, the 16-line message format (radiogram), and others.

Allied Communications Publications

Allied Communications Publications are documents developed by the Combined Communications-Electronics Board and NATO, which define the procedures for communicating in computer messaging, radiotelephony, radiotelegraph, radioteletype (RATT), air-to-ground signalling (panel signalling), and other forms of communications used by the armed forces of the five CCEB member countries and/or NATO.

Brevity code

Brevity codes are used in amateur radio, maritime, aviation and military communications. The codes are designed to convey complex information with a few words or codes. Some terms are classified to the public.

Morse code

Morse code is a character encoding scheme used in telecommunication that encodes text characters as standardized sequences of two different signal durations called dots and dashes or dits and dahs. Morse code is named for Samuel F. B. Morse, an inventor of the telegraph.

The International Morse Code encodes the 26 English letters A through Z, some non-English letters, the Arabic numerals and a small set of punctuation and procedural signals (prosigns). There is no distinction between upper and lower case letters. Each Morse code symbol is formed by a sequence of dots and dashes. The dot duration is the basic unit of time measurement in Morse code transmission. The duration of a dash is three times the duration of a dot. Each dot or dash within a character is followed by period of signal absence, called a space, equal to the dot duration. The letters of a word are separated by a space of duration equal to three dots, and the words are separated by a space equal to seven dots. To increase the efficiency of encoding, Morse code was designed so that the length of each symbol is approximately inverse to the frequency of occurrence in text of the English language character that it represents. Thus the most common letter in English, the letter "E", has the shortest code: a single dot. Because the Morse code elements are specified by proportion rather than specific time durations, the code is usually transmitted at the highest rate that the receiver is capable of decoding. The Morse code transmission rate (speed) is specified in groups per minute, commonly referred to as words per minute.Morse code is usually transmitted by on-off keying of an information carrying medium such as electric current, radio waves, visible light or sound waves. The current or wave is present during time period of the dot or dash and absent during the time between dots and dashes.Morse code can be memorized, and Morse code signalling in a form perceptible to the human senses, such as sound waves or visible light, can be directly interpreted by persons trained in the skill.Because many non-English natural languages use other than the 26 Roman letters, Morse alphabets have been developed for those languages.

In an emergency, Morse code can be generated by improvised methods such as turning a light on and off, tapping on an object or sounding a horn or whistle, making it one of the simplest and most versatile methods of telecommunication. The most common distress signal is SOS – three dots, three dashes, and three dots – internationally recognized by treaty.

Morse code abbreviations

Morse code abbreviations are used to speed up Morse communications by foreshortening textual words and phrases. Morse abbreviations are short forms representing normal textual words and phrases formed from some (fewer) characters borrowed from the words or phrases being abbreviated. Aside: Morse code abbreviations are not the same as prosigns. Morse abbreviations are composed of (normal) textual alpha-numeric character symbols with normal Morse code inter-character spacing; the character symbols in abbreviations, unlike the delineated character groups representing Morse code prosigns, are not "run together" or concatenated in the way most prosigns are formed.

From 1845 until well into the second half of the 20th century, commercial telegraphic code books were used to shorten telegrams, e.g. "Pascoela = Natives have plundered everything from the wreck". However, these are distinct from abbreviations.

The following Table of Morse code abbreviations and further references to Brevity codes such as 92 Code, Q code, Z code and R-S-T system serve to facilitate fast and efficient Morse code communications.

Prosigns for Morse code

Procedure signs or prosigns are shorthand signals used in radio telegraphy procedures, for the purpose of simplifying and standardizing communications related to radio operating issues among two or more radio operators. They are distinct from general Morse code abbreviations, which consist mainly of brevity codes that convey messages to other parties with greater speed and accuracy.

There are also specialized variations used in radio nets to manage transmission and formatting of messages. In this usage, Morse prosigns play a role similar to the role played by the nonprinting control characters of teleprinter and computer character set codes such as Baudot or ASCII.

The development of prosigns began in the 1860s for wired telegraphy. They are distinguished from common Morse abbreviations. Since Morse code communication preceded voice communications by several decades, many of the much older Morse prosigns have exact equivalent procedure words for use in the more recent radio telephony (voice).

Prosigns may be represented in printed material either by a sequence of dots and dashes, or by a sequence of letters, which, if sent without the normal inter-character spacing (concatenated), correspond to the prosign symbol.

QN Signals

The QN Signals are Morse code operating signals that were introduced for Amateur radio net operation in 1939 on the Michigan QMN Net to lighten the burdens of net control operators. Originally created by a committee of the Detroit Amateur Radio Association led by Ralph Thetreat, W8FX. Ev Battey W1UE (W4IA-SK), then ARRL assistant communications manager, later printed them in QST.The QN Signals are currently defined by the ARRL document FSD-218 and in the ARRL Operating Manual.Although these codes are within the Aeronautical Code signals range (QAA–QNZ) and thus conflict with official international Q signals beginning with QN, the ARRL informally queried FCC's legal branch about the conflict. The opinion then of the FCC was that "no difficulty was forseen as long as we continued to use them only in amateur nets."

QSA and QRK radio signal reports

The QSA code and QRK code are interrelated and complimentary signal reporting codes for use in wireless telegraphy (Morse code). An enhanced format, SINPO code, was published in the ITU Radio Regulations, Geneva, 1959, but is longer and unwieldy for use in the fast pace of Morse code communications.

Q code

The Q code is a standardized collection of three-letter codes all of which start with the letter "Q". It is an operating signal initially developed for commercial radiotelegraph communication and later adopted by other radio services, especially amateur radio. To distinguish the use of "Q" codes transmitted as questions from those transmitted as statements, operators used the Morse question "INT" (dit dit dah dit dah) as a prefix to the "Q" code.

Although Q codes were created when radio used Morse code exclusively, they continued to be employed after the introduction of voice transmissions. To avoid confusion, transmitter call signs are restricted; no country is ever issued an ITU prefix starting with "Q".

Codes in the range QAA–QNZ are reserved for aeronautical use; QOA–QQZ for maritime use and QRA–QUZ for all services.

"Q" has no official meaning, but it is sometimes assigned with a word with mnemonic value, such as "Queen's" (e.g. QFE = Queen's Field Elevation), "Query", "Question", or "reQuest".

Radio code

Radio code is a colloquial term that refers to any code that is commonly used over a telecommunication system.

Signal strength and readability report

A signal strength and readability report is a standardized format for reporting the strength radio signal and the readability (quality) of the radiotelephone (voice) or radiotelegraph (Morse code) signal transmitted by another station as received at the reporting station's location and by their radio station equipment. These report formats are usually designed for only one communications mode or the other, although a few are used for both telegraph and voice communications. All but one of these signal report formats involve the transmission of numbers.

Z code

Z Code (like Q Code and X Code) is a set of operating signals used in CW, TTY and RTTY radio communication. There are at three sets of Z-codes: one originally developed by Cable & Wireless Ltd. (the Cable & Wireless Service Z-Code) for commercial communications in the early days of wire and radio communications, one independently developed by NATO forces later for military needs and use, and one developed by APCO. The NATO Z Code is still in use today, and is published in the unclassified document ACP-131. There are other sets of codes internally used by Russia's military and other operating agencies. The old C&W Z Codes are not widely used today.

A lot of the old C&W codes are derived from mnemonics (ZAL = alter wavelength, ZAP = ack please, ZSF = send faster, etc.

Amateur and hobbyist
(aeronautical mobile)
Land-based commercial
and government mobile
Marine (shipboard)
Signaling /
Selective calling
System elements
and principles
Network topology
and switching

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