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The Other Amphibious Sherman Tank

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The Other Amphibious Sherman Tank

Postby Mil-tech Bard on 08 Jan 2010 20:59

This is the story of the T6 flotation device for the M-4 Sherman -- the rival for the DD drive system used so disasterously on D-Day in Normandy -- as told by Floyd Coleman, and ordnance enlisted man assigned to the project.

The T6 is also called the M19 device in "British and American Tanks of World War II" by Chamberlain and Ellis

There was a T7 floatation device for the M18 Hellcat and a M20 device for the m24 chaffee.

Some 250 were built for each vehicle type. Only the T6 was used in combat when 45 were launched on Marine tanks at Okinawa. Some were put in the water 10 miles (!) off the coast and still managed to get to shore.


See:

http://www.warriorsaga.com/

The Blankenship team assembled T-6 units and demonstrated them to various commanders. It fell to Lieutenant Coleman to give a presentation to General George Patton. He met with Patton and gave an oral explanation of the T-6 unit and how it worked. Patton was impressed with the concept and particularly with the idea of the infrantry being able to use the discarded flotation tanks as cover on the beach. He thanked Coleman and told him that he would be in touch as matters progressed with the invasion plans. Unbeknownst to the general public, Patton was only in command of a phantom army at this time. It was an elaborate deception against the Germans. It worked well, but Patton did not arrive in France until after the Normandy invasion, so he was not heard from again concerning the T-6 project.

By May 1944, the Supreme Allied Command authority decided against using the Blankenship T-6 system in favor of the Gruver system with the flotation skirt. Reason being that the Blankenship was 45 feet in length and reduced the number of M-4 tanks that could be transported by half. Coleman and his team were detailed to accompany the Gruver units as they made their landings on the Normandy beaches and report on their performance. Everyone drew their combat equipment and loaded on the LSTs along with the Gruver equipped M-4 Medium tanks. As the LSTs approached Normandy on June 6, 1944 (D-Day), the tanks were made ready for launching. A tragic oversight had been made with the Gruver systems. When they had been tested at various times, it was never with a fully loaded tank! The initial tests in the Chesapeake Bay had been with no ammunition on board, nor full fuel load, or full crew or crew equipment. The Chesapeake was smooth compared to the sea around Normandy. Now they were being launched with full ammo load, full fuel, full crew and crew equipment as well as additional essential spare parts on board. The first four tanks that were launched immediately foundered and sank taking most of their crews to the bottom with them!

Coleman realized what was happening and sought out the officer in charge of launching the tanks. He was a captain and Coleman told him he needed to stop launching the Gruver equipped tanks, he was just killing the men in them. He replied that his orders were to launch them and he would do so. Coleman went to find higher authority when he met a colonel coming his way who had realized the disaster in the making. He ordered the captain to cease launching the tanks. Other LSTs had similar experiences. Some tanks did make it to shore but the losses were very high. The remainder of the armor wasn’t unloaded until the LSTs could come close to the shore later in the landings. After the armor was ashore Coleman and his crew returned to England.

Back in England, Coleman’s crew continued to train the British on the use of the Blankenship T-6 systems, which were back in favor after the disaster with the Gruver system. There was some slack time during this period and Coleman and his crew spent several days in London. While there the British provided him with a chauffeur and a car. The chauffeur was a female British sergeant who had previously been Bob Hope’s chauffeur while he was on his USO Tours in England. She knew all the right places to go!
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Re: The Other Amphibious Sherman Tank

Postby binder001 on 08 Jan 2010 21:58

An interesting story. I didn't know the T6 would have been ready in time for DDay. I never heard of the "Gruver" device. The Duplex Drive is usually credited to Staussler. The Duplex Drive was developed by the British starting with the Valentine DD, then progressing to the Sherman V DD and Sherman III DD. By the time the US Army got into the act they were beneficiaries of a developed system. The US was given sets of DD plans and had their sets produced to the British designs. Firestone Tire and Rubber produced 350 sets of equipment that were applied to M4A1s then shipped to the UK for training. The US DD crews were given escape training. The tanks were tested and training was done at the Slapton Sands beaches before the three DD units (two medium tank companies each from three tank battalions) were deployed for DDay.
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Re: The Other Amphibious Sherman Tank

Postby Mil-tech Bard on 09 Jan 2010 06:53

IIRC, 100 of the 350 the American built DD kits were given to the British due to a lack of industrial capacity.

I am still looking for good information on the Ritchie devices outside of a Hunnicutt book.

What I am looking for is where these type classifications of M19 and M20 came from for the Sherman and Chaffee kits.


binder001 wrote:An interesting story. I didn't know the T6 would have been ready in time for DDay. I never heard of the "Gruver" device. The Duplex Drive is usually credited to Staussler. The Duplex Drive was developed by the British starting with the Valentine DD, then progressing to the Sherman V DD and Sherman III DD. By the time the US Army got into the act they were beneficiaries of a developed system. The US was given sets of DD plans and had their sets produced to the British designs. Firestone Tire and Rubber produced 350 sets of equipment that were applied to M4A1s then shipped to the UK for training. The US DD crews were given escape training. The tanks were tested and training was done at the Slapton Sands beaches before the three DD units (two medium tank companies each from three tank battalions) were deployed for DDay.
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Re: The Other Amphibious Sherman Tank

Postby Mil-tech Bard on 09 Jan 2010 18:54

Page 11 of "Amtracs: US amphibious assault vehicles" by Zaloga mentioned the M19 (T6 Ritchie) on 20 Shermans at Okinawa.

Page 265 of Camp Colt to Desert Storm: the history of U.S. armored forces, By George F. Hofmann, Donn Albert Starr, mentioned that 45 Marine Sherman's were fitted with T-6 Flotation devices

Page 265 of Camp Colt mentioned the USMC bought 10 M24 and tested them with "fording kit" in 1945 that sounded a lot like the M20 Ritchie device.
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Re: The Other Amphibious Sherman Tank

Postby Mil-tech Bard on 10 Jan 2010 17:55

Here are some more places I have found the Ritchie kits:

Pages 108 & 109, "US Military Vehicles: World War II," by E.J. Hoffschmidt and W.H. Tantum,

Pages 280, 281, 282, 319, 352 of "Marine tank battles in the Pacific," By Oscar E. Gilbert

Pages 97, 98, & 232 of "Marines under armor: the Marine Corps and the armored fighting vehicle, 1916-2000," By Kenneth W. Estes
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Re: The Other Amphibious Sherman Tank

Postby Mil-tech Bard on 22 Feb 2010 18:51

I have found on-line a report of a T8 device for the M26 Pershing that was tested in April 1946.

The general report was it could only be used from an LSD, because it was too long and too wide.
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Re: The Other Amphibious Sherman Tank

Postby Mil-tech Bard on 22 Feb 2010 21:19

This is what I found on the T8 device for the M26 Pershing.


The Armored Division as an assault landing force.
The Armored School.
May 52.

Pages 73-77

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...

PURPOSE :
To provide flotation equipment which will permit theMedium Tank, N26 to negotiate, under its own power, deeprivers and expanses of ocean.

HISTORY:
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.
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