Jay Leno doesn't just bring comedic firepower to any place he shows up ... he's bringing literal firepower, too -- 'cause he rolled around the L.A. streets in a freaking tank!

The comedian was caught by a couple locals driving slowly down a residential street ... with his head popping out the beast. Unclear if its the real deal or a ride tricked out to look like a tank -- but he's steering it like a pro, regardless.

It's outfitted with a massive gun ... though we doubt Jay could actually conquer any territories with it. However, it's certainly intimidating -- even if Leno isn't since he pulled over to have a fun convo with the dudes filming him.

General Leno jokes he's on patrol in the neighborhood ... keeping everyone safe in his new armored vehicle.

The guys ask him when he bought it ... and, it pays to make good friends clearly -- 'cause Jay says someone gave it to him as a gift!

Of course, Leno's got a pretty impressive car collection ... with everything from restored jalopies and vintage muscle cars -- to an old-school fire engine and a train on wheels!

Leno's also known for riding hogs too ... but, he's clearly going tactical with his new tank!!!