The North of Scotland Hydro-Electric Board owed its existence to Tom Johnston, who as wartime Secretary of State for Scotland pushed the Hydro-electric Development (Scotland) Act 1943 through Parliament. The idea was elegant: a public body would build hydro stations across the Highlands, sell bulk electricity to Lowland Scotland at a profit, and use that profit to electrify remote crofting communities at prices that did not reflect the real cost of stringing wires through empty country. The Board's first two major projects - Loch Sloy and Tummel-Garry - had faced fierce opposition from anglers, landowners, and amenity societies. The Shira scheme sat in nearly empty country, close to Sloy but tucked away in a valley that almost nobody visited, and protests were minor. The Board surveyed the area in 1946. The rain gauges recorded an annual average of 105 inches, with extraordinary bursts when fronts came in off the Atlantic.

The scheme would impound the River Shira to create Lochan Shira, with a smaller reservoir, Lochan Sron Mor, sitting below it. The main dam was a round-headed buttress design - chosen after consideration of several alternatives based on the variable rock strata at the dam site - 2,379 feet long and 148 feet high. Some 135,000 cubic yards of rock and soil had to be excavated before the foundations went in. The second dam was actually two structures joined either side of a rock intrusion: half concrete gravity, half earth fill with a concrete spine. Construction went well until mid-June 1954, when four months of relentless rain made working with earth fill nearly impossible. The crew kept going anyway. By the end of December 1954, impounding had begun in the lower reservoir, and the main reservoir filling started in December 1956.

From Lochan Sron Mor, a tunnel six miles long and eleven feet in diameter ran out under the hills to Clachan power station on the banks of Loch Fyne. Half the tunnel was excavated in the first year. The station itself presented a choice between a surface building and an underground one. Costs were similar, but steel was in short supply after the war and the underground option saved 350 tons of it. The cavern was excavated by cut-and-cover - dig the hall from the surface, build a reinforced concrete arch roof over the machine hall, then bury the whole thing under the original profile of the ground. It was the first large underground power station the Board built. Inside it, a single Francis turbine spun a 40 MW generator - the largest water-powered generator in the United Kingdom at the time. Clachan came online in January 1955.

Edward MacColl, the Hydro Board's first chief executive, had proposed a "reversible hydraulic station" at Loch Sloy back in 1936 while he was working for the Central Electricity Board. The idea was rejected as uneconomic. MacColl died in 1951, before he could see his concept built. Angus Fulton and Tom Lawrie, who drove the Board forward after MacColl's death, pushed pumped storage as a way to gather data for a coming nuclear era - reactors run best at constant output, and pumped storage gives a grid the buffer it needs to balance demand. Sron Mor station was the result. It normally generated power when water passed from the upper to the lower reservoir, but its lower reservoir was too small for the catchment. To prevent water going to waste, Sron Mor was fitted with pumps to push water from the lower reservoir back up to the upper one when capacity allowed. It began operating in autumn 1957, eighteen months before the dams were finished.

There was a third part of the scheme, off in the valley of the Allt na Lairige. Engineers wanted to build a dam there to feed a power station on the River Fyne, but a conventional mass gravity dam would have made the scheme uneconomic. Cheaper alternative: a prestressed concrete dam. Fulton went further: spend the same money on the prestressed design, but build it fourteen feet taller. It would be the first prestressed gravity dam of its type ever built anywhere. The risks were real - there was no precedent and no field data - but Fulton said the project had "an element of adventure" and the Board agreed to proceed. Construction Scheme No. 27 was published in 1953. The Allt na Lairige Dam was completed in autumn 1956, 1,395 feet long and 78 feet high, with a 1.75-mile tunnel feeding two Pelton wheels and a 6 MW generator on the Fyne shore. The dam was fitted with instruments to record how prestressed concrete behaved under load. The data went into future engineering. The Board never built another prestressed dam.