During the 1930s, Fascism was taking over in Europe and Hitler’s Nazi party was turning militarism and racial prejudice into a new religion.

Those who saw the writing on the wall got out to England or America and so as this riveting new play opens, we find J. R. Oppenheimer in America working on the bomb which would change the face of war forever.

Oppenheimer is quizzical, remote, charismatic and to some extent ruthless, resenting physical intimacy.

“Can’t you leave me alone!” he says to an over-possessive, alcoholic, mistress, who finally commits suicide.

Formerly a card-carrying Communist, an affiliation he prefers to forget in the highly watchful, politically prejudiced, world of American top security, where a black car is eternally parked watchfully in the street and where his phone is tapped.

“Were there any clicks on the line?” he asks a friend who calls him in Los Alamos, where the race to build the atomic bomb took place.

In and out of this dazzling re-construction of Oppenheimer’s world, re-imagined superbly well by its author, Tom Morton-Smith, a world with its bitching colleagues and its sexual free-wheeling and amorality, you get a distinct feeling that all the participating scientists, are far less concerned with the death of an individual Japanese citizen, than they are with the numerical equations sketched out on the blackboard.

At one point, when the effects of the blast are under discussion, we hear that two piles of carbon dust were once two human beings, but that notion is quickly submerged in talk of ratios of this and that, and the scientific rationale takes over once again and humanism is shelved.

Oppenheimer

“I don’t think anybody should have this weapon....not the United Nations....not America...nobody”, says a team-scientist who is against everything the atomic bomb stands for.

“You’re a child”, says Oppenheimer swiftly, “...the bomb must be used - and used on people...can you continue in your work, or will I have to reassign you?”.

This is a frequently disturbing play, where the opposing forces of morality and military strategy bring you to the edge of your seat, which is where you stay for most of the evening, as the author attempts to tell the story of a nation in crisis and where the bomb can be conflated, if you wish,with God the Destroyer, here conceived in unemotional numbers.

At the centre of all this horror is John Heffernan as J.R.Oppenheimer. Here is an actor who deserves any top award going for a performance which truly touches the heights and which is as perfect in its nuances, its light and shadow as anyone could wish it to be.

In a marvellous evening where the whole company is dazzling, (another jewel in this season’s already jewel-studded RSC crown) a special word should go to the equally dazzling designer, Robert Innes Hopkins, ( yes, the bomb does appear) who recreates so perfectly the America of the 1940s down to the immaculately-creased trousers of the men and the pastel-coloured linen suits of the women.

Runs at The Swan Theatre until March 7. Running time is 3 hours.