Warthunder occasionally has events where you can earn exclusive vehicles by completing certain tasks. A few weeks ago, they had D-Day themed event where you could earn a Churchill AVRE with the 290mm petard mortar.
Everyone and their dog is playing around with them now. They're generally quite useless in-game unless you get a city map. Even then, their slow drive speed, glacial reload speed, and 130m max gun range makes them very tough to use but damn, DollarPlays makes it look easy.