There seems to be some confusion here......
An ELT is an Emergency Location Transmitter.
It's a small package, used both on ships and aircraft.
It floats, and transmits radio waves. The frequencies used are 121.5 MHz and/or 406 MHz.
Nothing to do with VLF or ELF.
A ULB is an Underwater Location Beacon.
Its is attached to an FDR or CVR, and remains attached when the FDR or CVR sinks.
It transmits sound waves (pings), so the remarks about radio spectrum allocation are irrelevant.
Currently the sound frequency of the pings is about 30 kHz, but it has been suggested to lower this to about 9 kHz, to improve the detection.
CJ