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The American artist [[Samuel F. B. Morse|Samuel Morse]], the American [[physicist]] [[Joseph Henry]], and mechanical engineer [[Alfred Vail]] developed an [[electrical telegraph]] system. The simple "on or off" nature of its signals made it desirable to find a method of transmitting natural language using only electrical pulses and the silence between them. Around 1837, Morse therefore developed such a method, an early forerunner to the modern International Morse code.<ref name=Burns-2004/>{{rp|page=79}}
The Morse system for [[telegraphy]]
In his earliest design for a code, Morse had planned to transmit only numerals, and to use a codebook to look up each word according to the number which had been sent. However, the code was soon expanded by [[Alfred Vail]] in 1840 to include letters and special characters, so it could be used more generally. Vail estimated the [[letter frequency]] of English by counting the [[movable type]] he found in the [[Type case|type cases]] of a local newspaper in [[Morristown, New Jersey]].<ref name=Burns-2004/>{{rp|page=84}} The shorter marks were called "dots" and the longer ones "dashes", and the letters most commonly used were assigned the shortest sequences of dots and dashes. This code, first used in 1844, was what later became known as ''Morse landline code'', ''[[American Morse code]]'', or ''Railroad Morse'', until the end of railroad telegraphy in the U.S. in the 1970s.{{citation needed|date=May 2021}}
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|style="text-align:center;"| {{anchor|asterisk_anchor}}[*] || Codes that are ''not'' cut numbers, or are not numbers, are {{grey|'''shaded grey'''}} in the table.
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|style="text-align:center;"| {{anchor|dagger_anchor}}[†] || There are no distinct cut-number codes for '''{{small|4}}''' or '''{{small|6}}''', since cut numbers are made by reducing multiple ''dahs'' in the standard Morse number codes to only one ''dah'', but keeping all the ''dits'' as-is; digits '''{{small|4}}''' and '''{{small|6}}''' already
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|style="text-align:center;"| {{anchor|double_dagger_anchor}}[‡] || Some operators just send the standard code for '''{{small|5}}''', even when using other cut numbers, since five ''dits'' are still fairly short (same duration as {{nobr|cut '''{{small|3}}'''}} and {{nobr|cut '''{{small|7}}'''),}} and one might imagine a single ''dit'' possibly being misinterpreted as either a mistaken {{nobr|cut '''{{small|1}}'''}} or cut decimal point.{{citation needed|date=October 2023}}
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; Exclamation mark : There is no standard representation for the [[exclamation mark]] [''' ! '''], although the {{sc| {{overline|KW}} }} [[Digraph (orthography)|digraph]] ({{morse|dash|dot|dash|dot|dash|dash}}) was proposed in the 1980s by the [[Heathkit]] Company.{{efn|[[Heathkit]] was a popular, long-standing vendor of kits for amateur radio equipment.}} While Morse code translation software prefers the Heathkit version, on-air use is not yet universal, as some amateur radio operators in North America and the Caribbean continue to use the older {{sc| {{overline|MN}} }} digraph ({{morse|dash|dash|dash|dot}}){{efn|name=exclamation_note| {{sc| {{overline|MN}} }} or {{sc| {{overline|OE}} }}, {{morse|dash|dash|dash|dot}}, which some telegraphers unofficially use for an exclamation mark [''' ! '''], is shared with unofficial letters {{sc|Ö}}, {{sc|Ó}}, and {{sc|Ø}} used in some non-Latin alphabets.}} copied over from [[American Morse code|American Morse landline code]].
; Currency symbols : The ITU has never formally codified any [[currency symbol]]s into Morse code: The unambiguous [[ISO 4217]] currency codes are preferred for transmission (e.g. [[CNY]], [[EUR]], [[GBP]], [[JPY]], [[South Korean won|KRW]], [[USD]], etc.). However, the {{nobr|symbol [''' $ ''']}} was represented in the [[Phillips Code]]{{efn|The [[Phillips Code]] was a huge collection of abbreviations used on land line telegraphy.}} as two characters "'''{{sc|SX}}'''"; eventually operators dropped the intervening space and merged the two letter code or abbreviation into the single unofficial punctuation encoding {{sc| {{overline|SX}} }} ({{morse|dot|dot|dot|dash|dot|dot|dash}}).
; Ampersand [''' & '''] : The suggested unofficial encoding of the [[ampersand]] [''' & '''] sign listed above,{{efn|name=E_S_for_&_note}} often shown as {{sc| {{overline|AS}} }}, is also the official Morse [[Prosigns for Morse code|prosign]] for ''wait''. In addition, the [[American Morse code|American Morse encoding]] for an ampersand ({{morse|dot|aspace|dot|dot|dot}}) was similar to '''{{sc|ES}}''' ({{morse|dot}}{{morse|dot|dot|dot}}) and [[Amateur radio operators|hams]] have nearly universally carried over this use as an abbreviation for "and" (e.g. {{sc|WX HR COLD ES RAINY}} "the weather here is cold and rainy"). Since '''{{sc|ES}}''' is well established and slightly quicker than {{sc| {{overline|AS}} }}, there is no motivation for replacing it.
; Keyboard "at" sign [''' @ '''] : On 24 May 2004 – the 160th anniversary of the first public Morse telegraph transmission – the Radiocommunication Bureau of the International Telecommunication Union ([[ITU-R]]) formally added the [''' @ '''] ("[[commercial at]]" or "commat") character to the official Morse character set, using the sequence denoted by the {{sc| {{overline|AC}} }} digraph: {{morse|dot|dash|dash|dot|dash|dot}} .<ref name=ITU-R-M-1677/><ref name=ARRL-News-2003-12-10/>
: This sequence was reported to have been chosen to represent "A[t] C[ommercial]", or a {{nobr|letter 'a'}} inside a swirl represented by a {{nobr|letter 'C'.}} The new character facilitates sending [[email|e‑mail]] addresses by Morse code, and is notable since it is the first official addition to the Morse set of characters since [[World War I]].<ref name=ARRL-News-2003-12-10/>
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