This is what I found on the T8 device for the M26 Pershing.
The Armored Division as an assault landing force.
The Armored School.
Rigid Flotation Devies. A more rugged type offlotation device for the M4 medium tank, known as the T-6 wasemployed experimentally by Marine and Army tank units duringthe Okinawa landing.
...The T-6 consists essentially of six steel pontoons;one pontoon on each side of the tank, one on the bow, one onthe rear, with bow extension and rear extension pontoons whichhinge upward for more compact stowage prior to launching. Thesix pontoons are compartmented by sheet steel partitions intomany sub-compartments; Sub-compartments are filled withplastic foam-to further ensure buoyancy should the pontoons'bec one punctured.T-6 floated tanks are seaworthy, having been success-fully tested in twelve foot waves. The floated tank isfortythree feet long and therefore provides a fairlystable gun platofrm, enabling a tank gunner employing thegyrostabilizer to deliver accurate fire during the beachapproach. Compared with LVT(A)ts (amphibious tanks), thefloated tank constitutes a more stable gun platform; thehigher velocity and greater accuracy of the stabilizedtank gun in comparision with the LVT(A) howitzer and thetank's heavier armor, are important advantages. Pontoonsare jettisonable form inside the tank on reaching thebeach. Pontoons are remountable and can be reused.T-6 devices, as used on Okinawa, generally providedadequate flotation but needed further development to im-prove steering, to increase speed above the 42 knots ob-tained by the tank tracks revolving in the water, and toprovide a reverse...
Little modification has been made on this device. It is now called the M-19 Flotation Device by the Army. Some ofthe disadvantages are readily apparent in the specifications: Its length is 47 feet 8 inches, width 11 feet, and height 11 feet 8 inches (including exhaust and intake stack of waterproofIng kit) when prepared for launching. The front and rear out-boards can be folded upward to for loading, reducing the length to 33 feet 7 inches and increasing the height only two inches.
The weight of the flotation device is approximately 16 tons.No improvement has been made in manner of propulsion and thespeed remains about five miles per hour in water.4The same principle was employed in the development ofthe TS swimming device for the M-26 Tank, This model couldprobably be adapted very easily for use on the M-46 or M-47 tank. To compensate for the weight of the M-26 tank it wasnecessary to increase the length of the device to 65 feet andthe width to 14 feet. The weight of the device itself is 34,000pounds.5 Since this is the latest equipment built along this line the following extracts from the development report givesa good picture of its capabilities and limitations.
DESCRIPTION:....The Deive, T8 provides the means for floating the Medium Tank, M26 as a self-propelled unit. It consists of metal floats in four jettisonable assemblies with propulsion furnished by the vehicle tracks; steering is accomplished with two rudders.
...The rudders are manually operated by a crank handle in the driver's compartment which connect tothe rudders by chain and cable. The vehicle is equippedwith a standard fording kit...
To provide flotation equipment which will permit theMedium Tank, N26 to negotiate, under its own power, deeprivers and expanses of ocean.
The first test of the equipment was made at APG (Aberdeen Proving Ground,) 25 April 1946,..(The size and weight of the device poses a problem in logistics. Assembly under field conditions would be a major problem.It was recommended.. "No further development work should be carreid on with floating devices of this type for the Medium Tank M26, or other vehicles of equal or greater weight except as an expedient 5...
The rear extension and the width of the device make launching from the landing Ships impossible. They can only be launched from a ship of the LSD type which actually floatsthe tank inside the ship allowing it to move out under its own power.The poor speed and maneuverability in water of tanks equipped with this device might possibly be improved with theinstallation of removable propellers geared to each rear trackidler. This would enable the driver to speed up or slow downeither propeller by use of the normal tank steering as is donewith all water craft having two propellers.