"This ,painting was sponsored by Mr Gordon Howell, previously Production Director of VSEL and Managing Director of Cammel Lairds Shipbuilders,who has fond memories of the build of the Brazilian 'O' class submarines and many other Boats built in Barrow-in-Furness, Newcastle and Birkenhead"
2 x Admiralty Standard Range 16WS - ASR diesels. 3,680bhp 2 electric generators. 2560kw. 2 electric motors. 6000shp. 2 shafts.
Surface 12 knots, Submerged 17 knots.
9,000 nautical miles at 12 knots surfaced.
8 x 21 inch torpedo Tubes (6 bow.2 stern).
6 officers, 64 ratings
Tonelero was seriously damaged by fire whilst fitting out. She was towed to H.M. Dockyard Chatham to have the central 60 feet section of the pressure hull cut out and replaced. All electrical wiring was replaced, as this is where the fire first started. As a consequence, completion of the boat was delayed until 1978, making Tonelero the last "Oberon" to be completed for any Navy.
All three boats were given a mid-life modernisation in 1995 by the company HDW/FERROSTAL.
Hummaita was decommissioned in 1996. Riachuelo was decommissioned in 1997, and is now displayed at the Navy Cultural Centre in Reo de Janeiro.