The below was derived from one in a series of articles ('Classic Quotables') by Don Bishop at the Public Diplomacy Council website, which in turn cited me as the provisioner of the quote.
In late 1940, the State Department was concerned about 'anti-American propaganda being short-waved hourly to Latin America' and the Department of Justice was concerned whether 'Axis agents in the United States received direction and guidance from Nazi short-wave programs,' plus a growing concern about 'the growing aggressiveness of Japan as reflected in her radio broadcasts.' In addition to wanting to know what was coming into the United States, State, and others, saw foreign government broadcasts as a necessary insight.
Created at the suggestion of the State Department, and approved by the Board of War Communications, the Foreign Broadcast Intelligence Service (FBIS) was established under the Federal Communications Commission in March 1941. It was operation a few months later in June. It did not prepare or transmit domestic or international broadcasts. The purpose was to be the 'central agency serving all Government agencies requiring foreign broadcast material' by monitoring broadcasts from around the world and providing analysis on conditions in other nations. In part, the BBC's monitoring service validated the State Department request.
FBIS was monitoring the 'new media' of the day for national security, as the director of FBIS described in testimony in 1944.
Leigh's testimony was detailed and delved into Axis and Allied radio activities before and after December 1941. A small example:
Below is the list of languages FBIS monitored, as provided by Leigh at his testimony.