I hear the cops in Japan cross-train in Judo and Kendo.
Yes and no. The J-cops have their own version of police judo, which (unsurprisingly) is pretty heavy on arrest techniques.
Any additional martial arts that the police school applicants bring with them are highly encouraged.
And then, of course, there is the famous 1-year "angry white pajamas" Aikido course at Yoshinkan, which the riot cops have to take. A great business deal for Yoshinkan, may I add.