[...]
Readers of Tom Clancy's "The Hunt for Red October" can work out that the US
do indeed have something like this !   The commemorative transmission from
GBR a few weeks ago also formally clears the fact that we use 16kHz for our
comms links - hopefully I will no longer have to use the word allegedly when
stating this.
[...]

Not only the US do have such a system. For a page on the subject, with pointers
and photos, you can look here :   http://www.vlf.it/submarine/sbmarine.html

73  Alberto  I2PHD