“I’m going to see the President tomorrow,” Groves said. “He’s going to ask me why we need a test. We will have barely enough uranium for a single bomb, and we hardly have any plutonium at the moment. ‘Why should we waste any of it on a test?’ he’ll ask.”

“There are two separate devices,” Oppy said slowly and patiently, not because Groves was stupid but because he was not naturally articulate and these were the simple words Oppy wanted passed to Roosevelt. “There is the uranium device, which has basically a gun-barrel design. We don’t expect to have enough refined uranium until July, but we’re confident the device will work. Then there is the plutonium device, which has a complicated ‘implosion’ design. By July, we expect to have enough plutonium for two bombs, by August enough for two more, and by September plutonium for another two, but there is no certainty the design will work. It’s the plutonium device we have to test, and it’s the armory of plutonium devices that will end the war, not the single detonation of our uranium device. You can tell the President that choosing a test site is a sign of confidence.”

“We’re depending heavily on this site being right. The alternative test sites are some islands off California, sandbars off Texas, some dunes in Colorado. The last place I want to hide an atomic blast in is California,” Groves said.

“That depends on how big it is, of course,” Oppy said.

“Well, how big will it be?” Groves demanded.

“Five hundred tons of TNT is the current estimate of the yield,” Fuchs answered. He was along because he was part of the Theoretical Group estimating the blast.

“Couldn’t it be much larger?”

“Theoretically it could be five thousand tons, fifty thousand tons. Almost no limit.”

“Five hundred is a start.” Groves was mollified. “I’m going to tell the President we’re going to set it off on the Fourth of July.”

“Wonderful,” Oppy said.

Too bad we missed Christmas, Joe thought. Maybe this was the time to tell the general that the head of security on the Hill was of the considered opinion that Joe Stalin’s special agent was Robert Oppenheimer and they ought to pull off the road and get the whole thing sorted out. Even if there was nobody capable of taking Oppy’s place, and even if test, bomb and ultimate victory had to be scuttled. But maybe this wasn’t the time. Perhaps this was the best time to be a dumb sergeant, the “Indian companion.”

As soon as they hit the highway at Esperanza, Joe stepped on the gas. The wartime speed limit was 35 mph, but the general always preferred to cruise at 85. Gas rationing had largely emptied the roads, and the Buick could roll on a blacktop of two lanes, sometimes one, with wide shoulders for slow-moving donkey trains, carts, wagons.