Page "Surface wave" Paragraph 7

Most long-distance LF " longwave " radio communication ( between 30 kHz and 300 kHz ) is a result of groundwave propagation.

Mediumwave radio transmissions ( frequencies between 300 kHz and 3000 kHz ), including AM broadcast band, travel both as groundwaves and, for longer distances, as skywaves.

Ground losses become lower at lower frequencies, so the attenuation of ground waves decreases with frequency.

The VLF and LF frequencies are mostly used for military communications, especially with ships and submarines.