350.55 is a Royal Navy FOST frequency (Flag Officer Sea Training).
I heard it used during JW131.
"Warship ####" callsigns used on VHF Marine are generally the real name of the ship, because it is a public channel and anyone nearby could see the name of the ship thru a binocular anyway.
e.g. "Warship Argyll"
But on a NATO (230-399 Mhz) channel they would be more likely to use a tactical callsign such as "1 Yankee Zulu" or "Yankee 1 Zulu". In this case the callsign will be different today.
I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.