The last of Britain’s conventional submarines is being converted for use by the Canadians.

HMS Upholder, the first of the final class of diesel submarines operated by the Navy, is being prepared for the Royal Canadian Navy, transforming into the Victoria class boat Chicoutimi.

Shipbuilders BAE Systems have spent the past five years reactivating and overhauling Upholder and her three sisters, Unseen, Ursula and Unicorn, bringing them back up to operational status.

The four submarines, formerly based at HMS Dolphin in Gosport, were launched between 1986 and 1991, but were laid up in 1994, victims of the end of the Cold War.

The class was first mooted in the 1970s, and in 1979 the Type 2400 design was unveiled. The first boat was ordered from Vickers SEL late in 1983, with the other three ordered early in 1986.

Upholder-class boats displaced 2,455 tons when submerged, and had a complement of 47, seven of them officers.

The flotilla was sold to Canada in 1998, and their new owners have undertaken a programme of modification, including the installation of a new torpedo delivery and fire-control system.

Upholder emerged from BAE Systems’ Devonshire Dock Hall at their Barrow-in-Furness yard in Cumbria at the end of her revamp, ready to embark on an extensive programme of diving and sea trials through the autumn and winter.

This will include the commissioning of the main propulsion motor and diesel generators, work on the communications systems and periscopes, and testing and commissioning of sea water pumps.

Trim and basin dives are scheduled for next month, with sea trials commencing in the new year.

Although Upholder is the oldest of the class, she is the last to emerge from the refit process. She will assume the name Chicoutimi when she joins her sisters across the Atlantic – Unseen has become HMCS Victoria, Unicorn is now Windsor and Ursula is Cornerbrook.

“This has been a very successful programme for BAE Systems, and everyone who has worked on it can be justly proud of their achievements,” said BAE’s submarine division managing director Murray Easton.

“In some instances the scope of the work has been much greater than originally envisaged, but people have risen to the challenge, and have reinforced Barrow’s status as a submarine centre of excellence.

“We now look forward to completing the final phase of the work, and handing over a vessel which will provide the Canadian Navy with many years of excellent service.”

Upholder will be officially renamed and handed over to the RCN at Clyde Naval Base – Faslane – next spring.