Alan,

Then I saw that there was a wide hump of noise centred on 137 and
assume they switched to GMSK.

Here's a 1 kHz-wide shot of how it looks this morning.
http://webpages.charter.net/w1tag/files/cfh.jpg

It does take up some room, and even though the static crashes were a lot
fewer last night, I could not see my usual Loran lines around 137.774. I
have no way to know if that was due to the 137.0 signal, or not.

In any case, it was hardly the biggest disappointment of the day.

John Andrews, W1TAG