At the end of the 19th century the disparate units across any field were instantaneously joined to their commanders by the invention and mass production of the radio. At first the radio could only broadcast tones, so messages were sent via Morse code. The first field radios used by the United States Army saw action in the Spanish–American War (1898) and the Philippine Insurrection (1899–1902). At the same time as radios were deployed the field telephone was developed and made commercially viable. This caused a new signal occupation specialty to be developed: lineman.