"Enrico Fermi and Leo Szilard worked together at in 1939-40, just after was discovered, to ascertain the feasibility of a nuclear chain reaction, and then on the construction of the first nuclear reactor. Szilard believed a nuclear bomb could be built, and that the Germans may be doing so, but Fermi was sceptical. The Anglo-American project to build a bomb began late in 1941 after brought the to the attention of U. S. physicists. Szilard recalled "On matters scientific or technical there was rarely any disagreement [but] Fermi and I disagreed from the very start of our collaboration about every issue that involved not science but principles of action in the face of the approaching war. If the nation owes us gratitude — and it may not — it does so for having stuck it out together as long as was necessary." As the war with Germany was drawing to a close and the successful construction of the atomic bombs was well underway, these two men took opposing positions regarding use of the bombs."