Amazing Stories Volume 1, No. 3, June 1926. Source: Wikicommons
An unnamed marine biologist has requested the United Kingdom's Royal Navy provide documentation on
"abnormally large or dangerous sea monsters hundreds of metres under the sea"
but apparently the MoD doesn't centralize such reports, and the Freedom of Information office isn't going to seek out all such reports, for logistical reasons. (UK Press Association).
The real question is, who made the request, and what are they looking for? It's the Bloop, isn't it?
The contrast with the case of Loch Ness is notable. We have records of government discussions over how to protect Nessie legally, and that in the early years of the Nessie craze, local police believed in the existence of the creature, and worked with the national government to protect it.