No 5 is the Cattewater Branch  and Cattewater Junction is at the end of the curve

I am only a naturalised Janner having come to Plymouth in the 1976 from Paddington as a Railway Supervisor.
Part of my job included running Friary Yard and the Branches to Plymstock (formerly Yealmpton and Turnchapel) and Cattewater Harbour which joined at Cattewater Junction.
There is not much left now.  Friary is not much more than a run round loop,  Plymstock is closed and lifted and the Cattewater branch is out of use and has been lifted from  the Scrap Merchant just beyond the site of the junction.  No more Esso Fawley Tar Tanks, No More Fisons Fertiliser or Steel for Blight and White.  No more clay from Marsh Mills to Victoria Wharf or Cement from Blue Circle at Chelston Meadow to Chasewater and no more scrap for Severn Tunnel Junction or Government Stores for the Dockyard Trip.
The Cattewater is an arm of the sea from Mount Batten , past Turnchapel and Oreston towards Laira.

Yes indeed

I remember the Night Ferry using Platform 1 at Victoria. in the early 1970's
At that time there were folding screens between the canopy supports along the platform which I was led to believe was to isolate the platform for Customs and Immigration purposes.  Was this pre EEC ? as I do not see then in the picture of Victoria posted in this thread or were they nearer the stops.