In order to offset the loss of employees who became soldiers during World War II, the Post Office Department introduced the concept of a zoning address system in several large cities. Eventually this developed into the Zoning Improvement Plan ZIP Code system, and by July 1963, every home in the country had been assigned a 5-digit code. By the end of the 1960s, the US Post Office was struggling financially and reform was desperately needed. In 1970, comprehensive legislation was introduced and by 1971, the US Post Office was transformed into the United States Postal Service. The Postal Reorganization Act changed the face of the organization, particularly relating to its labor relations, financials and transportation. The USPS added four digits to the existing five-digit ZIP Codes in order to increase efficiency and speed of mail handling and delivery in 1983.