A Federal probation law was opposed by judges and the U.S. Justice Department. Opponents argued that the courts should not be turned into "maudlin reform associations...The place to do reforming is inside the walls and not with the law-breakers running loose in society." The tide of support for probation rose, however, as it became clear that the prison system was unable to manage a growing offender population and that a less costly alternative to incarceration for certain offenders was a practical necessity. The original Probation Act was passed in 1925. This article describes the provisions of the act as well as the 1930 amendments and the early expansion of the Federal probation service. One section of the article discusses the Judicial Conference's development of appointment qualification for probation officers in 1940. A section on probation officer in-service training considers the role of training institutes, a training center in the Northern District of Illinois, and training publications. Another section addresses the evolution of presentence investigations and supervision functions. The concluding section of the article focuses on the significant work performed by probation officers during World War II; they were engaged in many activities related to the war effort, such as helping selective service boards determine the acceptability of persons with convictions, dealing with violators of the Selective Service Act, assisting war industries in determining which persons convicted of offenses might be considered for employment, and supervising military parolees. 1 table, 6 notes, and 6 references