The Isle of Portland Unit was founded in 1956 and was designated Unit Number 483 under the Command of Lt G Mogford.  It has been providing opportunities for young people to gain experience for 50 years.

The Unit took its name from Admiral Sir William Penn (1644-1718), an English Quaker and founder of Pennsylvania, USA.  His "House", Pennsylvania Castle, used to be a major hotel on the island, but is now a private residence.  However, the owner still open the grounds for charitable events.

As well as Portland Unit, two commissioned Royal Navy vessels also bore the name Penn.  F19 saw active service from 1916 to 1921 and G77 saw active service from 1941 to 1948.

TS PENN's first headquarters started in a wooden hut outside the gates of Portland Naval Base in an area known as Boscawen, alongside the Elliot hanger (now demolished).  In 1981, owing to the re-development of the Boscawen site as the new Royal Navy sports complex, the Unit was moved to the top floor of the old NAAFI bakery in Castletown.  In 1984 with the increase in Unit strength, the Unit acquired the first floor of the building and later the ground floor as a boat store.

Portland Unit had a strong detachment of the Girls Nautical Training Contingent dating back to the 1960's  However, with the change in Sea Cadet policy in 1992, the GNTC were amalgamated into the SCC.

In 1995, with the closure of the Royal Navy Dockyard, the Unit moved to its present location at the Old NAAFI shop in Westcliff on top of the Island and continues to thrive.