A group fighting for the future of Devonport naval base has declared a battle for supremacy with Portsmouth.
Devonport is the sole UK refitter for nuclear missile submarines
A Ministry of Defence (MoD) review aims to reduce over-capacity and cut costs at Devonport, Portsmouth and Faslane.
Campaigners say that nuclear submarine base Faslane is unlikely to be affected, leaving a fight between Portsmouth and Plymouth.
Devonport backers say basing the surface fleet there would save £100m a year, compared with £25m at Portsmouth.
Devonport Management Limited (DML), the South West Regional Development Authority, county, city and district councils, and local MPs unveiled the figures in a document, Case for Devonport.
Founded in 1691
Sole UK refitting base for Vanguard nuclear missile-firing submarines
Home base of HMS Ocean
Devonport, western Europe's largest naval shipyard, employs 4,800 people in Plymouth and is the UK's sole refitting base for Vanguard submarines, which provide the UK's strategic nuclear deterrent with Trident nuclear missiles.
Dennis Gilbert, chief executive of DML said: "The ministry needs to save a substantial amount of money, we have compared ourselves and we think the case is overwhelming to keep Devonport as the southern naval base.
"Because of the nuclear infrastructure in Devonport, you can only reduce Devonport, the nuclear element is still going to be required.
Founded in 1194
Home to almost two-thirds of the Royal Navy's surface ships
Home base of HMS Ark Royal and HMS Victory
"At Portsmouth they don't have that same infrastructure; so the savings at Devonport are about £100m, whereas at Portsmouth it would be £25m.
"There is a substantial difference on economic grounds."
The results of the MoD review will be published next spring.
KBR, the majority shareholder of dockyard owners DML, was floated on the US stock exchange this week.
The MoD had asked it to withdraw the offering amid concern over whether KBR would have the cash to successfully run Devonport, given that it will no longer be able to rely on support from parent company Halliburton.
The MoD still has the right to take control of the dockyard at any time if it deems it to be in the essential security interests of the United Kingdom.
British naval ships and nuclear submarines, including Vanguard submarines, are maintained at the south coast dockyard, which is also run by Balfour Beatty and The Weir Group.