Lualualei VLF transmitter
VLF transmitter Lualualei is a facility of the United States Navy near Lualualei, Hawaii transmitting orders to submerged submarines in the very low frequency (VLF) range. == Description == VLF transmitter Lualualei operates under the callsign NPM on 21.4 kHz and 23.4 kHz.
Source: Wikipedia — Lualualei VLF transmitter (CC BY-SA 4.0)