Can battle tanks go under water?

Vietnam War M-48 Patton tanks could crawl on the bottom of rivers, to cross to the other side. But they had to be fitted with snorkels which fed air into their diesel 12 cylinder engines, as well as for the four crewmen (so they could breath).

The newly issued M-551 Sheridan light tank (officially designated the Armored Airborne Reconnaissance Assault Vehicle), which was designed in the very early 1960's, then manufactured in about 1967, landed in Vietnam in January 1969. Every US Armored Cavalry Squadron and the one regiment in Vietnam, the 11th ACR (Blackhorse) were soon equipped with this aluminum hulled tank (with a steel turret and 152mm gun). Even though the "long title" doesn't say "amphibious" or "swim capable"; the Sheridan was the only tank in the US Army that COULD SWIM! Not very good, but it could cross a river. In Vietnam they leaked and flooded, but with the bilge pumps on, if the river wasn't too wide, the Sheridan could do it. The M-551 weighed approximately 17 tons combat loaded (fuel and ammo); the M-48 weighed in a around 52 tons combat loaded. But the Patton was PURE 100% steel. The Sheridan was about 60% aluminum.