paddy wagon 
noun North American informal
A police van.The protesters refused, and a few minutes later the police arrived with a paddy wagon....
- Demonstrators attempted to prevent the arrest by blocking access to a police paddy wagon which had showed up to carry the mime away.
- All this time, the person is locked in the paddy wagon with the police standing around outside, talking to the medical staff.
Origin
1930s: paddy from Paddy, perhaps because formerly many American police officers were of Irish descent.