In 1915, newly developed panel switching systems were tested in the Mulberry and Waverly exchanges in Newark, New Jersey. When the technology first appeared in the Mulberry exchange, subscribers had no dials on their telephones and the new system was transparent to them — they asked an operator to ring their called party as usual. However, the operator keyed the number into the panel equipment, instead of making cord connections manually. The panel switch was later, from the early 1920s through the 1930s, installed in large metropolitan areas in the Bell System. By the 1950s twenty cities were served by this type of office.