The Super Apocalypse Tank is a rarely-seen but vastly improved version of the normal Apocalypse Tank used by Russia.
The rather unimaginatively-named Super Apocalypse bears many resemblances to an epic unit, including a massive HP pool (nearly ten times as much as the normal Apocalypse), immunity to most support superweapons and automated control, making it immune to mind control, hijacking and abduction. It is also amphibious.
The Super Apocalypse only appears twice in the game:
In Mad Monster, the Allies hack the control systems of the Super Apocalypses, turn them against their creators and use them to destroy an Apocalypse manufacturing complex. The objective of the mission is to infiltrate their Control Towers so the Soviets can't retake control of them and the Super Apocalypses will remain in Allied hands.
In Relentless, though not appeared, Super Apocalypse Tank is mentioned by Allied intel after three Apocalypse Tanks are destroyed, saying that Yuri did not have chance to control them.
In the Battlecity Challenge, Super Apocalypses appear every 15 minutes as reinforcements for the enemy Russian forces.
The Super Apocalypse bears a resemblance to the Super Tank from the Red Alert: The Aftermath mission Monster Tank Madness. Both are extremely powered-up versions of the most powerful tank in the Soviet arsenal, cannot be built or used by the player, are described in-universe as being fully-automated, and appear in a single Allied campaign mission in which the objective is to hack and reprogram them for use against the Soviets.