Beginning in 1913 the primary official time station broadcasting in the eastern United States was the Navy's NAA in Arlington, Virginia, however NAA was decommissioned in 1941. WWV began broadcasting second pulses in 1937, but initially these were not tied to actual time. In June 1944, the United States Naval Observatory allowed WWV to use the USNO's clock as a source for its time signals. Over a year later, in October 1945, WWV broadcast Morse code time announcements every five minutes. Voice announcements started on January 1, 1950, and were broadcast every five minutes. Audio frequencies of 600 Hz and 440 Hz were employed during alternating minutes. By this time, WWV was broadcasting on 2.5, 5, 10, 15, 20, 25, 30, and 35 MHz. The 30 and 35 MHz broadcasts ended in 1953.