Had not heard this story. Raspberry was a well known tactic, but thought it was developed by Johnny Walker.
https://time.com/5772665/uboat-wargames/?fbclid=IwAR3y3W6GX0VG-oFbXRfUMEUkyrOfy6YuwXqxBDwQYyAXnpuOMFiLpKFD2gM
Derby House, HQ Western Approaches, is well organized for visitors. Did not see the top floor, described in previous article.
http://www.39-45war.com/western.html