Sherman-vs-German Heavy Tanks-Bog Tendencies

[rexford]

During research conducted in dark corners of storage sheds throughout eastern New York State, a U.S. report was found where Shermans were actually less mobile on soft ground than Tigers and Panthers. Report stated that Tigers and Panthers moved over muddy ground that bogged or slowed down Shermans.

Results were attributed to narrow Sherman track and deficiencies in transmission gearing. Shermans equipped with track extenders did much better, and came close to matching Tiger/Panther flotation.

Ability to move over soft ground more than just ground pressure.

Will attempt to contact our special agents and obtain report from secret "FBI" files (Formerly Buried Information).

[Alexander]

Rexford, is this a subtle 'diss' of CM's lack of flotation modelling?

[Freak]

Keep it it comin rexford. I enjoy your informative posts. I dont see how these posts can be anything but helpful to BTS for further development in CM, even if he may be incorrect.

[rexford]

My notes indicate that Sherman inadequacies over soft ground may have been addressed in a special report was sent to Gen. Eisenhower on how American armor was comparing to German. Have sent out e-mails attempting to obtain scan of pages to supplement my notes, since my copy is now in Albany City landfill (accidentally placed in garbage years ago).

According to note, report included story where Panthers and Tigers completely outclassed Sherman over soft ground, due to narrow Sherman track and gearing (Sherman didn't have proper gear for softground?: isn't clear in notes).

"Superior flotation" mentioned in notes.

"Duck Bill" track extenders designed to address problem of inadequate soft ground movement by Shermans, and were successful.

Eisenhower report also states that Panther 75 had higher rate of fire than 75mm Sherman. "E" report may have also commented on blinding effect of 76mm muzzle blast, and we will look into this.

The report prepared for Eisenhower is very thick, and includes numerous cases where panzers fired on and hit Allied armor at 2000m and 2500m.

I played Advanced Squad Leader alot when we received the Eisenhower report, and tried to get them to decrease soft ground differences between Shermans, Panthers and Tigers.

Ground pressure is normally calculated as weight of tank divided by track area in contact with ground. For Sherman using data in Hunnicutt, average pressure under tracks is 33,350 pounds per track divided by (170" track contact length x 16.56" width), for 13.7 psi for M4A3 mid-production.

Measuring from my scale model Panther and treating a metric ton as 2200 pounds, 45,500 total metric tons weight equates to 50,050 pounds divided by (162" contact length x 24" width), for 12.9 psi. So Panther has slightly less ground pressure than M4A3 Sherman if I calculated correctly. Please correct me if I erred, ground pressure is not my specialty and I'am using 1/72 scale models for lengths and widths.

Sherman has six wheel locations in contact with ground from front to back. Panther has eight wheel locations in contact with ground from front to back, and there are more wheels per location (better and more uniform flotation).

Since tracks have some flexibility, it would seem that more wheel locations and more wheels per location would promote uniform load distribution, and peak load on ground under Panther track could be smaller percentage of total than Sherman, and add to Panther advantage over soft ground.

Better flotation could result in faster movement across soft ground.

[rexford]

Hunnicutt lists M4A3(75)W ground pressure as 14.3 psi, even higher than mid-production M4A3.

Would M4A3(76)W ground pressure be even higher?

Panther does not appear to be a particularly boggy type of vehicle, compared to Shermans, using tracks available in France. Of course, analysis is based on Panther scale models.

Flotation should be considered, as well as other factors that may apply. To ignore flotation is to miss something important enough to bring to Ike's attention.

[patboivin]

I have a question that I never could answer myself.

If the Tigers bog so much, why did some of them come with snorkels?!

[Bullethead]

Have you ever looked at the ground pressure values CM has for the various tanks in question here? The game uses nearly the exact same numbers you calculated here:

75mm Shermans, VVSS: 13.6 psi

76mm Shermans, VVSS: 15.1 psi

76mm Shermans, HVSS: 11.0 psi

Panthers: 12.5 psi

Tigers: 13.8 psi

King Tiger: 14.1 psi

So I think the game models ground pressure accurately for these tanks. Note that a King has a lower ground pressure than a VVSS 76mm Sherman

Anyway, a fairly easily available book that discusses (rants about, more like) the relative mobility of US and German tanks is "Death Traps" by Belton Cooper (he was a tank recovery/repair dude for 3AD in WW2). Cooper has nothing good at all to say about Shermans and points out repeatedly how Panthers and Tigers were able to move through mud that Shermans could not negotiate. He also mentions the duckbill track wideners but IIRC says they didn't work very well, primarily because they didn't stay on the tracks very long.

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-Bullethead

In wine there is wisdom, in beer there is strength, in water there is bacteria.

[Guest machineman]

This contains parts from the report you've mentioned, I believe:

http://www.hitechcreations.com/ubb/Forum9/HTML/000686.html

[Bullethead]

Just did a test of Shermans in the mud. I made a long, narrow map, lined up pairs of different types of Shermans at one end, and gave them fast move orders to the other end. I did this with both "mud" and "deep mud" conditions.

The main results are as follows:

1. The various Sherman models have a definite hierarchy of relative speeds in the mud;

2. VVSS Shermans bog down more often than HVSS Shermans. However, once bogged there seems to be an equal chance for both to become immobilized, and;

3. Among VVSS tanks, those with higher ground pressures bog more than those with lower pressures.

As to the 1st point, the different marks of Sherman always finish in the same order, shown below. All numbers are from the CM unit details box. Speeds shown are the stated max, although they were all obviously going much slower than this in the test.

1. M4A3E8(76)W - 32 mph, 37 tons, 11.0 psi

2. M4A3 - 32 mph, 33 tons, 13.6 psi

3. M4A3(75)W - 32 mph, 35 tons, 14.3 psi

4T. M4 - 24 mph, 33 tons, 13.6 psi

4T. M4A1 - 24 mph, 33 tons, 13.6 psi

5T. M4A1(76)W - 26 mph, 35 tons, 14.5 psi

5T. M4A3(76)W - 32 mph, 37 tons, 15.1 psi

The "Easy Eight" was BY FAR the fastest of the lot through mud, quickly pulling away to a commanding lead right off the start. In fact, even if it lost time being bogged, this tank could easily overtake the whole pack and regain the lead. The other tanks were much closer together in speed, it taking several turns to really start spreading them out enough to see which type was faster.

A couple of interesting things here. First, it seems that mud speed is a function of all 3 stats listed above. This seems evident because some heavier tanks with higher ground pressures were faster than some lighter tanks with lower top speeds. So maybe the Ford GAA of the A3s had more low end torque than the Continental of the M4 and A1, as well as a better top end? I don't know.

The other interesting thing is that the only difference in the stats between the fastest and slowest tank is the ground pressure. Thus, this variable seems to have the most effect on mud speed. So it seems that Rexford's question has been answered: higher flotation = higher speed in mud.

HOWEVER, regardless of how the numbers work together in the games model, I am not sure the specific numbers used in the game are all correct. For instance, I have the following numbers from U.S. Military Tracked Vehicles, by Fred Crimson:

M4A3(76)W - 35.5 tons

M4A3E8(76)W - 37 tons (with T66 track)

This is because the HVSS and the wider track it used were heavier than the standard VVSS and narrow track. I also have different numbers for some of the speeds of different models.

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-Bullethead

In wine there is wisdom, in beer there is strength, in water there is bacteria.

[Slapdragon]

As Rexford says, it seems more is involved in the bogging down of tanks than just ground pressure -- and reading cross country reports by the various militaries it seemed that each felt they had a problem. For the Allies, the heavier Shermans with Verticle Volute suspension were considered to have poor cross country ability from user experience. The Germans complained about the Tiger and the King Tiger along with a few of their tank hunters for bogging. The German Panther was considered one of the best cross country tanks in the world, only eualled (or in a few claims exceeded) by the E8 Sherman. The M18 Hellcat itself was considered by it crews in oral histories as "nearly unboggable", while the various light tanks in allied and axis use were good cross country vehicles. Note this is based on user complaints / praise and not upon any scientifc method.

Still, it appears that except for the heaviest tanks and the worst driving conditions, the primary reason for bogging was driver experience. In terms of CM there is one form of bogging: mud or snow bogging, which is the driving in of the treads of a tank the ground becomes a slick morass, leaving no traction and possibly causing a thrown track, damage to suspension, and immersion of the tread drive assemblies. Mud bogging was by no means the most common bogging. Other bogging included gully bogging, or attempting to cross a terrain feature that was to large to be crossed without dropping the tanks nose into a ditch, obstruction bogging, or riding over some for of obstruction, such as wood fenses, tree limbs, or other material that causes immobilization, wade bogging, or bogging while crossing a stream because the water's depth is misunderstood, and finally tippage, or literally tipping the tank over by driving one tread into a ditch or gully, or by moving at an unsafe angle up a hill (Arnold Swartzeneggar did this during his national service).

Most types of bogging, including mud bogging, seem to be effected bt crew experience more than small changes of ground pressure, flotation, or weight positioning. In fact, this may actually be the biggest variable in bogging, as can be shown by the statistics for bogging in off road races: were bogging is not associated with a single vehicle except when that vehicle is unusually in its size or weight, but with individual drivers (the same driver seems to bog more often) and how long they have been driving.

[Bullethead]

OK, I have now modified my test scenario by building a wall down the middle of it and putting some German tanks on the opposite side from the US tanks. Then me and Ariel ran it several times, enough to see the general trends.

In terms of speed across mud, the tanks rank as follows:

1. M4A3E8(76)W - 32 mph, 37 tons, 11.0 psi

2. Panther - 30 mph, 49 tons, 12.5 psi

3. M4A3 - 32 mph, 33 tons, 13.6 psi

4. M4A3(75)W - 32 mph, 35 tons, 14.3 psi

5T. M4 - 24 mph, 33 tons, 13.6 psi

5T. M4A1 - 24 mph, 33 tons, 13.6 psi

6T. M4A1(76)W - 26 mph, 35 tons, 14.5 psi

6T. M4A3(76)W - 32 mph, 37 tons, 15.1 psi

6T. Tiger - 23 mph, 63 tons, 13.8 psi

7. King Tiger - 22 mph, 77 tons, 14.1 psi

The Panther was only slightly faster than the 3rd place Sherman, IOW still well below the E8's speed. The King Tiger was only an RCH slower than the slowest Shermans and the Tiger I.

In other news, the German tanks all seemed less likely to bog than all US tanks except the E8, which had the lowest bog chance. Also, the German tanks appear less likely to become immobilized once bogged. Guess those wide tracks and interleaved roadwheels really do work

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-Bullethead

In wine there is wisdom, in beer there is strength, in water there is bacteria.

[jasoncawley@ameritech.net]

I would expect one other stat to matter for bogging, and for recovery once bogged - horsepower to weight. After all, many things that bogging represents are the kind of thing the tank has to pull itself out of, and its pulling ability is not measured by its ground pressure (which measures perhaps its traction or how deep it sinks), but by the ability of the engine to move the thing. That is the obvious reason, e.g. for the crews to report the M18 Hellcat as "unboggable". It has very high hp to weight. Whereas the Tiger I, even with reasonable ground pressure, is underpowered in this respect, with only ~10 hp per ton of weight. If the Tiger is already going, it may go through an obstruction, certainly. But once stopped or nearly so, the hp/weight is going to be a drawback, without question.

[rexford]

Thanks for responses.

[rexford]

The Eisenhower report noted in an earlier post on this thread was read (thanks for address), and Tigers are also noted as having better soft ground movement than Shermans. Royal Tigers compared to Shermans over soft ground and Tiger II sunk in less than Sherman.

Ground pressure is one thing, and uniform pressure is another. Tiger II has more wheels, larger wheels and more wheel locations and has to have more uniform ground pressure than Sherman.

If the Ike report is believed, Shermans with six wheel locations, made up of small wheels, would appear to have a higher PEAK ground point pressure than Tiger II.

[Michael Dorosh]

I am pretty sure duckbill track extenders were never a national secret - anyone who bought Tamiya's 1/35 M4A3 in the last 20 years has known about them.

Excellent point about them not staying on the tracks long - they tended to come off especially easy in urban terrain (ie pavement corners) but I suspect rocky ground as well - I hope no one is about to advocate that the game engine needs to track duckbill end connectors. We will all need P2000s soon!

Not being an armour buff, I am not sure what the difference between the Canadian pattern all metal Sherman track and the rubber chevron track was - would it have affected ground pressure?

[Bullethead]

FWIW, I added some PzIVs to this scenario. They all came in between the Panther and the fastest non-HVSS Shermans. That is, a tiny bit faster than the non-HVSS Shermans, but also only a tiny bit slower than Panthers. However, like the Panther, they seemed to have less tendency to bog than Shermans.

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-Bullethead

In wine there is wisdom, in beer there is strength, in water there is bacteria.