The 24m-long (79ft) Pin Wreck, named by Divers due to the large pins holding the copper hull to the wooden frame. The anchor standing upright to one end is of a mid 1800s design, so the wreck is thought to be post-1850.
The wreck is located south of Kimmeridgr was discovered in 1990.
Maritime archaeologists from Bournemouth University identified it as an Admiralty mooring lighter - a vessel carrying machinery for moving heavy loads.
The Bournemouth team dived into the wood and metal vessel, which lies 27m (88ft) deep, in 2019 after studying objects recovered in the 1990s by former university employee Nigel Bryant.
They included a ceramic fragment attached to a large pulley block marked "Portsmouth Dockyard".
Information from the dive suggested it was a naval mooring lighter from the mid-19th Century.
Researchers found records of two lighters from Portsmouth in the National Archives but there was no mention of their loss.
A breakthrough came in a copy of the Shipping Gazette from 11 September 1903, reporting the sinking of a mooring lighter off St Alban's Head, near Swanage, in rough weather while on tow from Portsmouth to Portland.
Thirty men had to transfer to its tug before it sank.
The wreck itself is upright on a sandy seabed at 28 m, which gives pretty good visibility. She is a very interesting wreck, yet very confusing. A set of machinery midships - a vertical capstan and associated cogs and worm gears plus a steam boiler and water tanks - but no sign of propulsion.
Originally it was suggested that it was some sort of work barge, which along with stories of a recovered military button and single diving boot have further confused wreck identification.