This topic grabbed my attention when I was looking for suitable reference pics on the TauchPanzer 111 (I've a Taigen TP 111 project waiting impatiently..) Somehow, I found myself diverted to pics of this Russian diving Tank, instead: the T-72 (Maybe it should be dubbed the 'U-72....

)
A few thoughts on the Tank:-
The mountings holding the Commander's observation tube to the turret, must have been incredibly strong. Water weighs around 1 ton for every cubic meter, and so that Commander's conning tube would have had to have withstood scary external forces, when cutting through the flow (especially if the river was flowing swiftly

).
It must have taken quite a while to fit the Commander's viewing tube, especially as it doesn't look as if the Tank could transport it in the prone position. (Support truck needed?) The snorkel for the engine could be put in place in 20 mins., apparently, and ready for action in two.
Did the crew have any form of escape breathing apparatus, of the type that used to be issued to submarine crews?
If the driver had a beef with the commander, he could always 'forget' the CO was perched up there, as the tank entered the trees beside the river.....
In a way, the Observation tube could be useful in a very hull-down position; but would have needed a tree-branch or bush disguise, or the CO would have been easy for a sniper to notch up.

This T-72A has the snorkel neatly stowed on the rear of the turret. I guess the snorkel has a telescopic action, when extending
Here's the T-72 with a snorkel, at Bovington. This version could cope with rivers that were 5mtrs deep (16'4')

"Get your facts first, and then you can distort them as much as you please"- Mark Twain.