The old marine band used to be from about 2-3 MHz. They stopped using it for
ship-shore comms back in the 70's when they went to VHF.

In the 1980s, that MHF band became a requirement again, but on usb. In fact, an
auto alarm requirement was added. A two-tine signal is sent.

2182 kHz is the calling and emergency frequency. 2638 is the most common
general use frequency in that band.

Bill, K5BY