Once again, the octagonal oak dining table had been pressed into service as a base of operations for the secret project which, if successful, would revolutionise public transport, reduce the dependence of bus fleets on diesel or, worse, petrol fuels (which were expensive and polluting).

Once again, dinner would be served on trays in armchairs as the plans, notebooks and slide-rules were deemed too valuable to move for such a minor interruption.

It was the latter part of 1972 and outside the house, only a tiny team at Rolls-Royce Engineering in Crewe, Cheshire knew about the discussions. Could liquid petroleum gas (LPG) be used to power a bus? Rolls Royce had an engine running on natural gas in their works driving a power plant on test, but the technology was not available to them to make it mobile. With very few adjustments it could be made to run on LPG.

LPG is a by-product of crude petroleum refining and at that time was made up of about 70% butane and 30% propane, with the precise proportions depending in ultimate purpose. The specification could be tightly controlled. North Sea natural gas had only 1% butane / propane proportions. Some US oilfields could reach 20% but this differed from well to well and even over the life of a well. Today, there are many different types of gas going through trials and even in use.

The world was in the middle of a fuel crisis: prices were rising inexorably and public transport, already subsidised, was not only costing national and local governments more, but fares on the buses were also going up thereby affecting millions of people every day. There was also the first signs of environmental pressure to reduce the harmful exhaust emissions on vehicles, particularly in towns .

Rolls-Royce had been considering an LPG powered engine for some time - but it took a discussion between Teesside Municipal Transport (TMT) Chief Engineer Roy Cotterill and his brother-in-law Lionel Gibbs, a Marketing Executive at Rolls-Royce, to create the realisation that RR had something that had the potential to revolutionise public transport.

Several months earlier, Roy had told Lionel that the price of diesel oil was causing significant problems for the industry. Lionel simply asked "what if you didn't have to use diesel?" Having a favourable answer, he returned to Crewe and immediately proposed to the product development team that he and Roy undertake a feasibility study - could the RR development engine fit in the engine bay of the most common buses - the Leyland Atlantean and the Daimler Fleetline.

The scope for market development was huge for these two buses formed the backbone of the global double decker bus market. If the project was successful, the potential for converting existing vehicles was enormous whilst licensing the engines to both Leyland and Daimler for insertion into new vehicles would also create a large new market.

Rolls-Royce were not as convinced of the value of the project as Lionel who, after all, had not been able to openly discuss it with Roy and so had only the broadest concept to present. "You can go ahead and produce a feasibility study," Lionel was told. "But you have to do it in your own time."

That would not have been much of a burden if it hadn't been for the geography involved: Crewe is in the North-West of England and Teesside is in the North-East. And the roads connecting the two were - indeed remain - winding roads through the Pennine Hills so that a typical journey was half a day each way, especially in winter. There was a motorway across the Hills but it was a long way around.

Lionel turned up with a bundle of plans. "It's a secret," he said. "Take a look at this."

Roy was amazed: the engine was smaller and lighter than the existing unit: physical modifications to the engine bay would not be extensive and there would be a weight dividend.

"It's almost silent when it's running," said Lionel. "The only noise your bus will make is from rattling panels!" Roy humphed - rattling panels are an inevitable side effect of the vibration of the engine. "And as the engine hardly vibrates, there will be a lot less of that, too."

Roy's interest was aroused: depending on the fuel consumption (which was difficult to calculate as bus use is different to any other form of use - a largely urban cycle with a very frequent stop-start and periods of running at tickover) and the price of the fuel the advantages of less vibration (therefore less maintenance of parts that work loose) and less noise (both in the workshop and in streets where, for example, a route or, worse, a terminus is in a residential area) were extremely valuable concerns.

"I’ll have a word at work," said Roy.

The response of the senior management at Teesside Municipal Transport was muted but supportive. The authority was already cash-strapped because its funding came from local government which had a political agenda that required extensive routing to be provided at minimal cost. Public transport was a social service not a commercial enterprise but funding was always difficult to prise out of the Council. An R&D project would be impossible to fund.

So if Roy wanted to play inventor, he could do so on his own time. But he could have a bus to play with if he could come up with the money to pay for the time spent in converting the bus - and putting it back into its original state.

Roy and Lionel decided that their employers had given enough of a green light for them to do some more work and at RR the Chief Engineer became involved – meaning that at least some of the meetings were now in Cheshire, not far from the factory where the chassis were made and the bodybuilder who turned them into buses.

The technical challenges were, in summary quite simple: remove the existing engine, modify the engine bay, change the fuel tank, insert the new engine and mate it to the transmission.

Anyone who has ever taken any mechanical device apart knows one thing: the first time you put it back together, it never goes back together in the same way or without some part being discovered on the floor during sweeping up.

Over a period of months, calculations of gearing, design of what would today be called "interfaces" and manufacture of parts were all discussed at RR and then brought back to Teesside with both men squeezing time out of busy work days and family life.

In Teesside the family was lucky: the project was happening all around them and it was exciting. In Cheshire, there were just absences as "dad" shot off to Teesside whenever possible.

Out of hours visits to the workshop became commonplace for both men as they lined up the various components - but they still didn't have an engine because RR had not released the "secret" tag. And they still didn't have a development budget.

At some point, one of the men mumbled something about getting government money and a light went on. Several weeks later, after a series of presentations and meetings, mostly held in secret because of the potential military application of the RR Engine, the then government gave a grant to the project. With that commitment, RR agreed to cover any difference in operating costs.

The money was to convert one bus, to run it for a year including lending it to other local government-owned public transport systems for evaluation, where feasible, because lack of suitable refuelling points would limit where the test could take place, and to reconvert it at the end of the year if TMT and RR decided that was what they would do.

By this time, the secret was now out as the TMT Committee were required to give their full approval to such a radical project. And so a Daimler Fleetline went into the corner site of a workshop at RR, reversed into place so that the minimum was visible to any passer-by and its engine and transmission removed.

The gearbox was retained in its original state, but a multi link chain reduction box was used to drop the drive line by some 8 inches and change all differential input rpm`s (revolutions per minute – the engine speed) to the standard.

The diesel tank was replaced with four tanks for LPG. Then the new engine was fitted. A range of new instrumentation had been designed and now added to, or replaced, most of the dials normally found in the cab.

The fuel tank was charged and the engine primed and started.

It was indeed almost silent and with the bus at rest, the time when the panels vibrate most violently, hardly moved at all. A handkerchief held over the exhaust pipe (a completely new system had been designed and fabricated) showed absolutely no black spots.

The bus was taken out onto the road: the test driver brought it back after a short trip. He was shaking. "It's terrifying," he said.

Read Part 2 at Part 2