A paddy wagon is a vehicle used by police to transport large groups of people who have been arrested.
"Paddy" is a common Irish name and was used as a pejorative with which to insult Irish people. Irish men overwhelmingly populated early police forces in many American cities, e.g., New York City, which was at one time host to two competing police forces. This concentration of Irish in the police forces could have led to the term "paddy wagon" being created.
Some theorize that the backs of these vehicles were often filled with rowdy, fighting drunkards. Irish people have also been stereotyped in this regard, which may have also contributed to the term.
These vehicles were usually painted dark black in color. Archaicly in the United States these vehicles were also called Black Marias ("ma-RYE-uhs"), a term still used modernly in parts of Britain for the vehicle that transports prisoners from jail to the courthouse.
[1]
See also
