During the Vietnam War, they were giant tanks that drove around the jungle. Using coconuts as ammunition. The term "Gorilla Tank" comes from the fact that many gorillas would grab onto these tanks as they drove by. The reason for this was that these tanks can reach speed of up to 120mph, and these gorillas love it. As a defense mechanism, these tanks could stop suddenly, forcing the gorillas off and to hit any target ahead of them.
Back in Nam one of them got dern Gorilla Tanks killed my best pal Hank.