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Testing the British Cruisers


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The_Chieftain #1 Posted Mar 06 2014 - 18:32

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Way back when, the US Army received a Centaur (T121154) and a Cromwell (T184085) from the British Army for testing. They ran them in comparison tests against a handy M4A3 (#12099). These were early production vehicles, equipped with 6pr guns instead of the 75mm which was added in the main production variants. They looked kindof similar to this:

 

Unfortunately, the report I found had no pictures :(. The various results and conclusions were as follows, in no particular order.

 

Determination of Limits of Vision.

Observation of the limits of vision indicates that in the buttoned up position, the British and American tanks offer approximately the same visibility. However, when driving with the hatch doors open, much better visibility can be had from Medium Tank M4A3 than from the British Tanks.

 

Determination of Obstacle Crossing Ability.

Both the Cromwell and Centaur bridged a distance of 96” forward and backward. Medium Tank M4A3 bridged 99” forward and 96” backward. Both the Cromwell and Centaur successfully negotiated a 36” vertical obstacle forward. Medium Tank M4A3 had difficulty in negotiating a 24” obstacle. All three vehicles successfully negotiated the standard concrete shell hole contour. All three vehicles negotiated the standard mud course with exceptional ease.

 

Determination of Fording Ability.

All three vehicles can ford satisfactorily 48” of water at minimum speed.

 

Determination of Turning Characteristrics.

The minimum turning diameter of Medium Tank M4A3 is 70’6”. Both of the British tanks have minimum turning diameters varying from 38’ in first gear to 235’ in fifth gear.

 

Slope operation:

Medium tank M4A3 and the Cromwell tank successfully negotiated the standard 60% slope. No attempt was made to try the Centaur tank over any slope above 30% at the request of the engine manufacturer. A new oil sump for the engine was installed to enable the vehicle to drive up the 60% slope, but the tests were terminated before this was done.

 

Firing Tests.

Better results were obtained with the Cromwell tank because of looseness in the fire control instruments in the Medium Tank M4A3

 

Operation in Sand, Snow and Mud.

Operation in the standard sand course indicated that in deep sand, Medium Tank M4A3 is more maneuverable than either of the British tanks because of its higher ground clearance and method of steering. All three vehicles operated satisfactorily in mud. No snow was available during this test programme.

 

Determination of maximum speed.

Cromwell: 39.7mph, reached in 32 seconds.

Centaur: 29.8mph in 40 seconds.

M4A3: 25.4mph in 32 seconds.

 

Drawbar Figures

Cromwell: Drawbar pull, 2nd gear: 18,375lbs at 5.2mph. 420hp at 11.2mph. Resistance to traction, 52lb/ton at 20mph.

Centaur: Drawbar pull, 2nd gear: 15,800lbs at 6.2mph. 306hp at 7.8mph. Resistance to traction, 58lb/ton at 20mph.

M4A3: Drawbar pull, 23,200lbs at 4.8mph. 324hp at 5.6mph. Resistance to traction, 73lb/ton at 20mph.

 

Continuous Operation Tests.

Both the British Cromwell and Medium Tank M4A3 have successfully completed 14 hours of continuous operation. Faulty air cleaners and a dusty clutch prevented the Centaur tank from completing 14 hours.

 

During the duration of this testing programme, the following approximate man-hours for extra maintenance was required on each of the vehicles. The time is based on actual repair on replacements only, and does not include time required to procure or manufacture spare parts not available. A complete breakdown by components for each of the three vehicles of the maintenance required is in an appendix. [Chieftain: To save space, I’ve turned it into a PDF file, https://worldoftanks.com/dcont/fb/document/cromcentshermmaint.pdf ]

 

Medium Tank M4A3: 39 man-hours.

Cromwell Tank: 199 man-hours

Centaur Tank: 202 man-hours.

 

Overall the conclusions were more or less as follows. Quotes follow:

  1. Since both the Centaur and Medium Tank M4A3 have the same power plant they are comparable; The Rolls Royce engine in the Cromwell tank appears to be a satisfactory engine installation and delivers more power than the Ford engine. However, although no great difficulty was encountered during tests, the accessories, ignition and oiling systems are more complicated than those on the Ford engine. [Chieftain's Note: This Centaur was one of the few equipped with the Ford GAY, which Leyland was pushing for at the time]
  2. The transmission on the Medium Tank M4A3 gave much better performance than the Merritt-Brown transmission in the British tanks, as several times during tests considerable difficulty was encountered with this latter transmission. However, some advantage is gained in the Merritt-Brown transmission since it allows the vehicle to be maneuvered more readily under certain circumstances, particularly when turning in close quarters.
  3. The hydraulic steering controls on both British tanks are unsatisfactory because of the amount of maintenance work required to keep them functioning properly.
  4. The hull and turret of both British tanks apparently do not offer an equal amount of protection to the crew as Medium Tank M4A3 since they are of riveted and bolted construction and offer large areas normal to ground fire.
  5. Range tables indicate that the 6-pounder gun in the British tanks, while superior to the 75mm gun in the Medium Tank M4A3 at shorter ranges, is inferior at longer ranges.
  6. Frequent tensioning is required for the track of both British tanks to keep them tight. Medium Tanks require tensioning also, but not nearly as much as the British tanks.
  7. The Christie type suspensions on the British tanks offer a very smooth easy ride under most conditions; however, on certain special conditions particularly on traversing two adjacent anti-clines, riding in the vehicle becomes almost inbearable to the occupants. While the medium tank M4A3 does not ride as smooth most of the time it is not subject to the harsh jolts received on the British tanks under these conditions.
  8. Firing tests indicated that the British system of fire control, particularly insofar as the direct telescope is concerned, may be superior to that of the Medium Tank M4A3.
  9. Both of the British tanks can be operated at higher speeds than the Medium Tank M4A3, but during tests very few conditions were encountered where this high speed could be utilized to any advantage. Drawbar performance of the three vehicles was somewhat comparable; however, the Medium Tank M4A3 seemed to be slightly superior when considering the power plants and weights of the three vehicles.

Final conclusion:

Based upon the results of the tests conducted at this station, it is concluded that, in general, both of the British tanks are inferior to the Medium Tank M4A3. This inferiority is displayed particularly in the lack of mechanical reliability in either of the British tanks, and a theoretical comparison indicates that the Medium Tank M4 is better protected and offers more firepower than either rof the British tanks.

 

Recommendation:

It is recommended that Medium Tank M4A3 be considered superior to the British Centaur and British Cromwell tanks without further testing.

A couple of observations.

 

The first one is the firepower difference. These were early versions of the vehicle, and the 6pr was very quickly upgraded to a 75mm similar to that of the M4, so that distinction is fairly irrelevant in hindsight. (Of course, the M4A3 got upgunned later, as well, so the argument can work both ways). Incidentally, the supposed better AP performance of the 6pr was why it was considered by the TD branch to replace the 75mm on the halftracks, only to be discarded after testing indicated that this advantage was for short range only. The comment about 'loose' fire control is interesting, no detail was provided as to if it was a general design flaw (unlikely) or just that one particular tank.

 

The second, the difference of armor. Yes, the M4 may have been overall slightly better protected, but realistically, what would the armour stop on M4A3 which would not be stopped by Cromwell?

On the other hand, the difference in speed is likely correctly de-emphasised. It matches with what Harry Yeide stated about the extra speed on the M18, that field reports indicated no tactical advantage was attained by the higher theoretical speed. Which, if you think about it, makes sense. You aren't likely to be running around the battlefield at top speed, you never know what's around the next corner or behind the next bush.

 

I find it difficult to believe that the US Army testers were unaware of the neutral steer capability of the British tanks. It's in the manual, and it's quite likely that over several hundred miles of testing someone would have accidentally discovered it anyway. Regardless, the substantially better mobility in close quarters was noted anyway, so little change in emphasis should be applied even if one considers the difference.

 

The killer, though, is the mechanical reliability. Those aren't typos above, the report actually does say about 40 man-hours for the US tank, and some 200 for both the British ones, not counting routine maintenance like track tensioning, also in M4's favour. This is a really big deal when you start talking about entire battalions of vehicles and the man-hours required of the REME/Ordnance folks supporting them. Again, it may not be entirely fair in this test report: The M4A3 was a working serial production vehicle, itself derived from a previous serial production vehicle, the Medium Tank M3. The two British tanks were pretty much brand, spanking new designs, teething problems would be inevitable.

 

Given, however, that there seemed little that the British designs had over the M4 in the other features, even if -all- the teething bugs got worked out, it seems there would still be little practical advantage to choosing Cromwell or Centaur over M4 anyway. Other than the fact that the British factories could produce the latter two, of course.

 

Again, I have to say that I would be very curious to see the British equivalent to this comparison test.



Kyphe #2 Posted Mar 08 2014 - 14:23

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The greater visibility was no doubt due to the Sherman's height, but that also means easier to spot and a bigger target to hit, the Russians found the Sherman to be top heavy and fell over on lateral inclines.

 

As for the maintenance It possibly the best thing about the Sherman that it was so easy to fix in the field, It has been said you can not get a real reliability figure on breakdowns due to tanks being fixed so fast that they were never recorded as being out of service at all.

 

But as for the maintenance of the Cromwell, were these US personnel tinkering with tanks they had no familiarity with? I would expect higher maintenance time due to the Christie suspension and the hydraulic steering alone but that still appears a little much.

 

Ofc if you ask brit tankies of the time though they liked certain aspects of the Cromwell they much preferred the Sherman, and anyone who has ever been inside either with know why.


Edited by Kyphe, Mar 08 2014 - 14:24.


Xamon #3 Posted Mar 08 2014 - 16:41

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If you notice, a lot of the maintenance on the cromwell is from someone "accidentally" backing the tank into a river. If you remove all the man hours for those repairs it is probably much more comparable to the M4. I mean you have breaks and idlers and suspension etc all damaged by this, that is a lot of man hours to fix.

Pooch #4 Posted Mar 08 2014 - 16:42

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All said and done I have to agree with Kyphe as to the US crews working on and unfamiliar tank, as some think I can contest to as back in the 90's as a tanker  going  from sister regiment to sister regiment working on  new tank.

 

P>S as to lack  of love on Facebook  who needs Facebook I don't.


Edited by Pooch, Mar 08 2014 - 16:45.


Dominatus #5 Posted Mar 08 2014 - 16:45

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I'd rather suspect that even if the US crews were unfamiliar with the Cromwell/Centaur, the British would have had a liason officer around to help them.

Xlucine #6 Posted Mar 08 2014 - 17:12

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View PostThe_Chieftain, on Mar 06 2014 - 17:32, said:

 
  1. Since both the Centaur and Medium Tank M4A3 have the same power plant they are comparable;

 

 

View PostXamon, on Mar 08 2014 - 15:41, said:

If you notice, a lot of the maintenance on the cromwell is from someone "accidentally" backing the tank into a river. If you remove all the man hours for those repairs it is probably much more comparable to the M4. I mean you have breaks and idlers and suspension etc all damaged by this, that is a lot of man hours to fix.

 

Not really, it's only 7 items of maintenance out of 43 total.



Kyphe #7 Posted Mar 08 2014 - 17:51

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View PostDominatus, on Mar 08 2014 - 1608 2014 - 16:45, said:

I'd rather suspect that even if the US crews were unfamiliar with the Cromwell/Centaur, the British would have had a liason officer around to help them.


Not the same as having familiarity of a whole maintenance crew is it though, lots of stopping and asking and sucking air through teeth and scratching of headsFree via Skype


Edited by Kyphe, Mar 08 2014 - 17:51.


Anlushac11 #8 Posted Mar 08 2014 - 18:19

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I was confused on the engines as well. Not sure why they would be considered the same unless referring to power output.

 

Centaur was to use a Nuffield-Liberty V12 rated for 340hp.

 

M4A3 used a Ford GAA V-8 rated for 450hp. Maybe referring to earlier M4A1 with radial engine rated at 400hp?

 

Cromwell used a Rolls Royce Meteor which was a detuned Merlin aircraft engine rated at 600hp.


Edited by Anlushac11, Mar 08 2014 - 18:22.


collimatrix #9 Posted Mar 08 2014 - 18:43

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It's almost like the US evaluators couldn't wrap their head around the idea of the steering drives receiving power when the gearbox is in neutral.

 

Of course the tank won't move if it's in neutral!  It's in neutral!                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                



The_Chieftain #10 Posted Mar 08 2014 - 20:38

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I have edited the article to explain one minor detail about the Centaur, which in hindsight I should have copped: This particular one was equipped with the Ford GAY, which was Leyland's choice. The War Office nixed the idea in July 1943.

LonelyGuardian #11 Posted Mar 08 2014 - 21:06

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...The American tanks are known for crew comfort, and the armor WAS better, however I do point out the minor fact that these are American tests, and unfortunately in strongly nationalistic times (like recently with Tom Clancy's novels) there is naturally hurr durr our country stronk syndrome

TheGunBunny #12 Posted Mar 08 2014 - 21:10

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Love how no one can say the M4 was a good tank.. Maybe it was...

 



The_Chieftain #13 Posted Mar 08 2014 - 21:12

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View Postcollimatrix, on Mar 08 2014 - 17:43, said:

It's almost like the US evaluators couldn't wrap their head around the idea of the steering drives receiving power when the gearbox is in neutral.

 

Of course the tank won't move if it's in neutral!  It's in neutral!                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

 

I don't see where you're getting that from.

 

I think there are several things which may de-emphasise the effect of the unfamiliarity the US testers had with the foreign equipment.

 

Firstly, WWII tanks are mechanically pretty simple things. It doesn't take too much to figure out what component does what, or how to replace this, that or the other. Secondly, we're not talking about sending Cromwell/Centaur to a line battalion and having standard mechanics try to work on it. The primary job of the mechanics at Aberdeen is to work on unfamiliar, non-standard equipment, be it of foreign or domestic manufacture. They probably have some pretty good analytical processes and techniques. (And working on something as common as an M4A3 may be unfamiliar to them!). And, thirdly, of course, both the manufacturer and the British Tank Mission would have had representation of some sort there as well. So, yes, unfamiliarity would have been an issue, but even if it ended up doubling the man-hours, which I doubt, you still end up with over twice the man-hours used.

 

Finally, even if one ignores the 'accidental descent into riverbed', there still seems to be more squawks on the British than American tanks. Which brings us back to the question of how many of those are effectively teething problems. An answer to which I do not know. But, again, the British vehicles would apparently have to run to even less than 40 man-hours in order to have any apparent notable advantage over M4.



The_Chieftain #14 Posted Mar 08 2014 - 21:17

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View PostLonelyGuardian, on Mar 08 2014 - 20:06, said:

...The American tanks are known for crew comfort, and the armor WAS better, however I do point out the minor fact that these are American tests, and unfortunately in strongly nationalistic times (like recently with Tom Clancy's novels) there is naturally hurr durr our country stronk syndrome

 

I don't know if that's really true. The Aberdeen testing process tends to be fairly objective. If the hydraulic steering took more man-hours to service than Sherman's, then there's not really much way of room for national bias there. And it's not as if I haven't seen Aberdeen reports be scathing of American equipment either. In comparison testing such as this, or the Firefly/M4(76) last month, the British equipment is going up against the best the US had to offer, after having been selected and developed through its own process to become the 'US Standard.'



Kyphe #15 Posted Mar 08 2014 - 21:40

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Again one does have to admit that these transitional British vehicles had some maintenance issues that they never really resolved. issues both in terms of particular systems chosen and lets not forget the difficulty of getting access inside the vehicles to work on parts of the steering for example and working in very confined spaces once you do.

 

Ofc If these were brand new vehicles then even British mechanics would not have had the time to work out best practice routines and there would have been a lot of ironing out of kinks to do.

 

It is not surprising though as when you look at the T21/25 program and the Pershing the various new systems they tried out all came with huge maintenance problems

 

But even when the Cromwell was operating at peak I personally as a brit would not choose it over the Sherman, even the comet is pushing it as there are some huge design flaws in the comet like access to the turret ring being covered by the recess for the gun, so I agree with the conclusions of the report despite the Sherman itself rapidly becoming an obsolete design.

 

 



1SLUGGO1 #16 Posted Mar 08 2014 - 21:46

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Very interesting, thanks for the post.  I knew there were debates about producing British vehicles and Aircraft in the US, but was not aware of the length of testing they conducted.

collimatrix #17 Posted Mar 09 2014 - 00:30

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View PostThe_Chieftain, on Mar 08 2014 - 21:12, said:

 

I don't see where you're getting that from.

 

The fact that they apparently didn't know it could neutral steer for a 0 meter minimum turn radius.

 

I was just guessing, but it's not like the Americans would have likely seen a double or triple differential gearbox before.



Frostopper #18 Posted Mar 09 2014 - 00:48

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View PostXamon, on Mar 08 2014 - 16:41, said:

If you notice, a lot of the maintenance on the cromwell is from someone "accidentally" backing the tank into a river. If you remove all the man hours for those repairs it is probably much more comparable to the M4. I mean you have breaks and idlers and suspension etc all damaged by this, that is a lot of man hours to fix.
You mean, all maintnace that occured on Crommie's odometer reading of 733?

 

Resaults, paraphrased:

Left Axle bent: Was removed and true'd in machine-shop

Right Axle bent beyond hope of repair: replaced.

Left track broke/snapped and busted an entire road-wheel assembly, replaced

'Hull-drain' popped, flooding fighting compartment, getting oil into the drum-brakes. Hole plugged and brakes replaced

Left idler bent out of alignment and siezed-up: replaced.

 

Incident @ 733 was probably caused by it slipping out of gear on a mere 20% descent similar to the one @ 421 miles, "no action taken".

@ 617 and 731 there were also notes on re-occuring difficulty steering due to hydraulic failures.

Steering-Brakes had to be re-tuned at 150 mile intervals (335, 432, and 506) somehow they then managed to go from 506 miles to 733 (233 miles) before the accident; however, at that interval they were doing their darndest to increase the hydraulic-pressure on those brakes.

-There is also quite the possability they did not re-tighten the brakes because they were too worn, and didn't want to waste time replacing them unless necessary (because it likely had already racked-up 100 maintnance-hours), so make it grip tighter and warn the driver (meanwhile, a similar near-accident happened on a parked centaur sliding down a 20% grade towards same riverbed).

 

So the accident was likely exactly such, from lack of experiance using/maintaining that particular tank*. In short, it was so fast downhill it drifted into the drink in a powerslide worthy of a T-50-2... Followed by an unmanned TOG-boat...

-which would've been awesome had they filmed it.

*Maintnance issue caught the maintnance-crew and their british advisors by surprise, and a nasty surprise, indicating they didn't maintain it enough as it was, even with 4x the man-hours.

 

Meanwhile Centaur was treated ginger like a lady and still gave trouble despite having 'bout the same engine as the M4A3.

-Centaur stopping brakes @ 528 miles

 

Lesson: British Tanks + American Maintnance = Funny.
-Because America is more like Russia that way.


Edited by Frostopper, Mar 09 2014 - 01:24.


Chopa #19 Posted Mar 09 2014 - 01:04

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On the subject of maintenance, there was this old boy who worked in the warehouse at MAN-VW in Swindon when I was there back in the 80's who had been a troop sergeant with the Desert Rats. He'd run the gamut of the British tanks we'd used in N Africa, then been issued with yank tanks. Despite the horror stories he told me about multibanks that spontaneously combusted, and having to drop inaccessible spark plugs on worn-out continental R975 engines to drain the oil out the combustion chambers of the lower cylinders to prevent hydro-locking on start up, he preferred the American-made tanks hands down when it came to repair and maintenance.

 

He said that less than 2% of their days would be spent in combat, but well over 98% would be spent in repair and maintenance!



Anchobi #20 Posted Mar 09 2014 - 01:34

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