The atomic bombs that the United States dropped on Hiroshima and Nagasaki stand out as major moments in history books, both as testaments to science and as proof of changing military strategy. But it wasn’t always certain that scientists in the U.S. would be able to make such strides. During World War II, many were terrified that Germany would be the first to build an atomic weapon.

Sam Kean, a science writer and the author of "The Bastard Brigade: The True Story of the Renegade Scientists and Spies Who Sabotaged the Nazi Atomic Bomb," writes about the tireless efforts to stop Adolf Hitler’s scientists from developing a weapon that could have turned the tide of the war in the blink of an eye.

“The discoveries that led to the atomic bomb, most importantly the discovery of uranium fission, happened right before the war started,” Kean said. These major advances in science — which, at any other time, might have only made a stir in academic circles — quickly gained the attention of both Allied and Axis governments.

And not only were these discoveries a really big deal, for science and the impending war, but most of them were made in Nazi Germany. “They actually had a big head start on the U.S. and the Allies in atomic fission research,” Kean said. “A full two years before we even founded our Manhattan Project, they founded the Uranium Club, which was basically the same thing.”

With Germany already enjoying a head start, and focused on building an atomic reactor, many scientists in Allied countries became convinced that Germany would soon build an atomic weapon.

“All of these rumors were leaking out,” Kean said about German progress on building a reactor. “And they were feeding this fear that the scientists already had.” They couldn’t just sit by and wait for Hitler to order a nuclear bomb strike on the United States.

“That fear of Adolf Hitler getting a bomb is what really drove the Manhattan Project,” Kean said. “If they hadn’t been so afraid, I don’t know if they would have pushed themselves so hard. They might not have actually finished by the end of the war, if they hadn’t been so afraid of Germany.”

The U.S. couldn’t only do their own scientific research, though — they had to make sure they weren't being outpaced by the Germans. Thus, the Alsos Mission, or “the Bastard Brigade,” was born. Given that name because they lacked any official parent organization, the members of the team relished the notion that they were renegades. “They were a hard-charging sort of group, running behind enemy lines, getting fired at,” Kean said. “They enjoyed the reckless atmosphere.”

The members of the Alsos Mission, including Joe Kennedy, Jr. and former Red Sox player Moe Berg, pursued intelligence on German scientific projects until the end of the war. “The risk of Adolf Hitler was so big,” Kean said, “that they could not let up on this.”

The work of the Bastard Brigade, with their complete commitment to the issue of nuclear bomb development, helped assuage fears and allow others, like General Dwight Eisenhower, to focus on other important military considerations. Without them, who knows how World War II would have ended.

Emily Greffenius is an intern at Innovation Hub. Follow her on Twitter: @emilyrg98