MFV's are smally craft well in need of a mother ship when present in large numbers, as they were during the war years.

That 'mother ship', officially called a TENDER, could have been issued with HMS MANDATE's callsign suitably amended.  Administrators, always civilians, just don't think do they?

On the other hand, HMS MANDATE might have been such a vessel!

Her callsign M V F T which could have been altered to M F V T.