Considered the first modern hand-held, self-contained, radio transceiver the SCR-536 was developed in 1940 and by July 1941 was in mass production. Colloquially referred to as a “walkie talkie,” the Galvin Manufacturing Corporation (turned Motorola in 1947) originally designated it as a “handie talkie” – the terms are often confused as the original walkie-talkie referred to the back mounted model SCR-300 voice radio receiver/ transmitter. Weighing in at 5 lbs. there was no external power switch on the SCR-536. The operator pulled out or pushed in the antenna on the top which operated an internal switch to turn the radio on or off. The range of the unit varied with terrain; from a few hundred feet (about 100 metres), to one mile (1.5 km).