Both the United States and other Allied countries censored mail to and from the United States, including mail to and from members of the armed forces. They employed examiners who literally opened and read private letters to ensure that no information deemed contrary to the execution of the war effort was included within them. They also placed certain individuals deemed suspects on blacklists, which meant their mail was automatically opened and read.
An obvious point of similarity between the PATRIOT Act and these measures is the fact that act strengthened the government's ability to access emails that may be relevant to investigation. Internet service providers could be subpoenaed and forced to disclose such information. While not exactly analogous to the massive censorship effort that took place during World War II (and most other major wars) the Act did raise some of the same questions about the propriety of government scrutiny of private communications.