<P> The codes, developed in 1937 and expanded in 1974 by the Association of Public - Safety Communications Officials - International (APCO), allow brevity and standardization of message traffic . They have historically been widely used by law enforcement officers in North America, but, due to the lack of standardization, in 2006 the U.S. federal government recommended they be discontinued in favor of everyday language . </P> <P> APCO first proposed Morse code brevity codes in the June 1935 issue of The APCO Bulletin, which were adapted from the procedure symbols of the U.S. Navy . </P> <P> The development of the APCO Ten Signals began in 1937 to reduce use of speech on the radio at a time when police radio channels were limited . Credit for inventing the codes goes to Charles "Charlie" Hopper, communications director for the Illinois State Police, District 10 in Pesotum, Illinois . Hopper had been involved in radio for years and realized there was a need to abbreviate transmissions on State Police bands . Experienced radio operators knew the first syllable of a transmission was frequently not understood because of quirks in early electronics technology . Radios in the 1930s were based on vacuum tubes powered by a small motor - generator called a dynamotor . The dynamotor took from 1 / 10 to 1 / 4 of a second to "spin up" to full power . Police officers were trained to push the microphone button, then pause briefly before speaking; however, sometimes they would forget to wait . Preceding each code with "ten -" gave the radio transmitter time to reach full power . An APCO Bulletin of January 1940 lists codes assigned as part of standardization; </P> <P> The Ten Signals were included in APCO Project Two (1967), "Public Safety Standard Operating Procedures Manual", published as study cards in APCO Project 4 (1973), "Ten Signal Cards", and then revised in APCO Project 14 (1974). </P>

Where does the term ten four come from