Upgrading Rosyth's dry docks - built for servicing the vast coal fired ironclads of the early 20th Century - so as to satisfy the most exacting safety standards applied to nuclear powered submarines involved meticulously argued design concepts coupled with intricate heavy construction work.
The hazard against which the project has to provide guaranteed protection is of a one in 10,000 year seismic event occurring at the moment that nuclear fuel is being lifted in or out of a submarine - imparting a horizontal acceleration of some 0.25 gravity to the dock, lifting apparatus and vessel.
Theoretical exploration of possible failure modes was so complex that proving the design and safety case, together with the project management, swallowed up nearly a quarter of the total expenditure on the work.
Buildings had to be cleared from around the legs of a vast dockside crane and an impact cage built to protect them in the event of other structures being felled by an earthquake. Plant such as the massive pumps and the pipework for salt water cooling of the reactors of a docked submarine, had to be extensively modified and doubled up to ensure failsafe operation after a major earthquake.
A world first is claimed for a vast rubber-mounted cradle which can support a vessel weighing up to 6,000t and isolate it from ground induced vibration. A submarine was in dock for a refit when the 1,200t reinforced concrete slab table was cast. To fit in with the tightly programmed refit schedule - which demands extensive rebuilding of each submarine after a decade at sea - the table had to be cast on one side of the dock floor and slid sideways to fit in with the departure and arrival of the submarines.
The client's Superintendent of Ships, John Lister, summed up the achievement of the safety case theoretically and actually: 'The day we wanted it, the dock was ready on time with all the ticks in the boxes.'