A device that played prerecorded Morse code for training radio operators in the U.S. military. The message is encoded in an ink pattern on paper tape. As it passes, the tape is illuminated from the top by a light bulb and read by a photocell under the tape. The tone sounds when the light is blocked by the black ink. Only one side of the tape is read. The tape is wound onto a reel on the motorized "puller," which pulls the tape through the reader.

The device was invented by Theodore McElroy during World War II. McElroy had founded the McElroy Manufacturing Corp. in 1941 to make telegraph keys and automatic telegraph equipment. The company sold to all branches of the U.S. military and was very successful.

McElroy became a professional Morse operator at the age of 15. He was highly skilled and in 1939 established a world record for receiving and decoding Morse code: 75.2 words per minute (Pierpont 2001).