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The US Army Tests Firefly


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The_Chieftain #1 Posted 18 January 2014 - 07:00 AM

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There are various stories going around about how the US Army was foolish for not either buying 17pr guns from the British to implement into their M4s, or, if British and Canadian production wasn’t up to it, simply building the guns themselves. However, almost all the documentation on the matter is either speculative or unscientific. It seems to be rather difficult to find an honest, objective assessment of the various options of tank armament to replace the 75mm. The commonly referred to tests conducted in Europe in the Summer of 1944 (See US Guns German Armor Part 1) were generally not very scientific “Let’s lob a few rounds at these Panthers we found and see what happens” type tests, and almost entirely focused on penetration characteristics which generally resulted in “17 pr may be somewhat better, but there is no practical achievement from that better” (i.e couldn’t reliably kill a Panther from the front any more than anything else)

 

Of course, there is far more to a proper, thorough test of a weapon system than field tests, and those tests are conducted at proving grounds. A review of such a more comprehensive series of tests may at least provide some understanding of US Army thinking on the matter, and if the US Army’s testing was valid, may allow one to consider the commonly heard refrain that Firefly Sherman was Best Sherman during the war.

 

A Firefly turret was made available to the United States Ordnance Department during the winter of 1943-44 and was tested at the Aberdeen Proving Ground against the 90mm Gun, M3, which at that time was emerging at the armament for Gun Motor Carriage M36, and was later to be mounted on Heavy Tank, T26E1 (the predecessor of Medium Tank, M26). As a result of these trials, the 17-pounder gun was considered by the Ordnance Department to be generally inferior to the 90mm gun.

 

Of course, that’s not entirely a fair test. The 90mm gun was being put into use as a tank destroyer, and in the next generation tank. But Firefly was being made to put the gun into the current generation tank.  As a result, more testing would be required to find out just how good a solution it would be for Sherman compared to the route chosen by US Army Ordnance. It was also only a test by the Ordnance folks, not the end users. Shortly after the war ended Army Ground Forces instructed that such a test take place, although supply issues (not least the delivery of several hundred rounds of British ammunition) resulted in the testing in Fort Knox by Armored Force and Tank Destroyer Board not being complete and written up until August of 1946. By this stage, of course, there was no longer any question of if the Firefly should be considered as a useful variant of M4 for acquisition; these were to be tests more focused on design features and its utility as an overall system to determine future tank design philosophy.

 



 

The vehicle as tested was the installation of the imported M4 17pr MkVII turret onto a standard M4A3 VVSS hull, so not a true Firefly conversion, but issues such as hull stowage were not really part of the tests and the merits of keeping the fifth crewman and bow gun were not debated. Three tank configurations were compared: The Firefly turret was compared with the M4(76) and M26.

 

The installations were comparatively rated on 21 characteristics. (If you are surprised by this number, ask yourself why. You think there isn’t something more to a tank gun than simply how accurate it is, how fast it shoots, and how much damage it does on the other end?) The report is quite long, so we’ll cover some of them in this article, and the rest over the next couple of weeks.

 

Without further ado, let’s go through the tests in the sequence as they appear.

 

Test 1: Handling and Loading Ammunition.

The rounds used, left to right: 76mm HVAP, HE, APC. 17pr SVDS, APC, HE, APCBC, 90mm HVAP, HE, APC.

 

Although the 17pr rounds are far from the longest, they are almost as wide as the 90mm rounds, making them the middleweight of the three. HE shells for the 76mm/17pr/90mm were 22.23/34.2/42.04 pounds, with the APC rounds at 24.8/37.5/43.87 and the supervelocity ammo being 18.9/28.41/36.25. Though the 17pr ammo was in excess of the proscribed US Army standards of the maximum weight a 3” caliber round should be, it wasn’t by much and the report noted that the round was not difficult to handle.

 

The problem of course is that handling the round isn’t the only issue. As the report stated:

Loading must be considered from the standpoint not only of weight and length of the round, but also loader’s working space. This space in the 17-pounder gun turret is particularly restricted, inasmuch as the loader must guide the projectile into the cutaway portion of the breech ring by movement in a horizontal plane in order for the base of the round to clear the rear of the recoil guard. In medium tank M26, the loader not being restricted by the recoil guard, is able to approach the breech with more latitude.[…] The advantage in weight and length of round of 17-pounder ammunition about equals the advantage of better working space in the 90mm gun turret, it is therefore concluded that ease of loading is substantially the same for both. In Medium Tank M4A3 with 76mm Gun M1A2, the advantage in weight and length of round, together with ample working space for the loader make ease of loading superior to the other two tanks

 

Loading 17-pounder


After trying a few loaders out, with times varying from 1.1 seconds (standing, round in hand) to 3.2 seconds (standing, round on floor) to get an average and to find the best loader, they tried for a ‘mad minute’. The crew were able to fire 8 rounds in 44 seconds.  The report notes, however, that “The 17-pounder gun rate of ten rounds per minute, computed from the actual firing of 8 rounds in 44 seconds, should be qualified by the understanding that this was done by a man of exceptional skill and that for the average man the rate will be nearer to 8 rounds per minute”. It also points out that as the Sherman VC ready rack only holds five rounds, such a rate is also unlikely. Further, it was also considered to be faster than the TC and gunner could sense and correct rounds at ranges under 2,000 yards. The 90mm was rated at 8rpm, (with ten ready rounds), and the M4(76) at 20rpm, although with only 6 ready rounds.

 

Certainly a tight fit between the recoil guard, turret ring and back wall.

 


Test 2: Dispersion.

 

The purpose of this test was “to test the dispersion of various types of 17-pounder ammunition at ranges from 500 to 2,000 yards, and to compare the result with similar data computed from 76mm and 90mm ammunition"

 

This was done by setting up 6’x6’ canvas panels at 500 yard intervals, and firing ten-round groups at them. 

APCBC at 500 yards.

 

Then they tried APCBC at 1,000 yards.

 

This successfully completed, they went back to the 500 yard target and fired SVDS.

 

Results were rated "poor", with 8 rounds on target, and two sensed as being about 36” below the panel, but for the purposes of calculation they were presumed to have the same average deflection as the 8 rounds that were on target. Overall deflection was 2.35mil, 4.34mil elevation, with means of 0.5mil and 0.92mil respectively.

 

Then they tried at 1,000 yards. After firing 18 rounds trying to register, (Successive rounds with the same sight picture were observed as over, left, short)  they decided to abandon further testing of the round except for armour penetration.

 

After firing the 28 rounds SVDS, they decided to go back to APCBC. However, the SVDS rounds had left duralumin fouling in the gun tube, and so before resuming the dispersion testing at range, they fired ten rounds of HE and then ten rounds of APCBC through the tube for the obscuration tests to clean it out. Given the observed results of the grouping (see “Phase B, below), they went back and fired another ten rounds of HE and APCBC. After the 40 rounds had been fired (Phase D), it was considered that the tube had returned to normal, (albeit at apparently a new zero) and the accuracy testing continued at 1,500 yards after an adjustment on the sights on a clean zero panel.

 

 

Figures for 1,500 yards and 2,000 yards were as follows. It is interesting to note that the size of the shot group was, in real terms, about the same as that at 1,000 yards, with a substantial increase at 2,000 yards. No explanation for this is offered in the report (It just reports test reports, not theories!), but the obvious thought from my unitiated mind is an oscillating trajectory caused by an unstable round which happens to have a wavelength which 'zeros' at about 1,500 yards. Of course, this is speculation on my part.

 

 

So, the average at all ranges was calculated to be 7.38mil/7.58mil overall, and means of .189mil and .205mil. The testing complete, they then dug into the records to find the test results of 90mm and 76mm guns.

 

Mean dispersions for deflection and elevation were .115mil/.142mil for the 90mm and .112 and .110 for the 76mm respectively.

 It was thus concluded that a “comparison of data shows that the 17pounder gun has greater dispersion than either the 90mm gun or the 76mm gun

 

 

That's plenty for part 1, so we'll return to these tests at a future point.





rash2000 #2 Posted 19 January 2014 - 11:59 AM

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yay i am first to comment!!!

 

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DanLBob #3 Posted 19 January 2014 - 12:40 PM

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So the last part of that final table says 44-45% increase in dispersion when compared to average in service gunners for the 76mm and 90mm. But I guess since only expert gunners where used to test the 17pdr then if the Firefly option had entered service the observed results would have been more inline with the expert test, ie 65-100% greater.

 

Interesting stuff Chieftain, I hope it won't be too long for part 2. 

 

DanJar


Edited by DanLBob, 19 January 2014 - 12:41 PM.


notsonooby #4 Posted 19 January 2014 - 01:33 PM

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Ill repeat the famous question: when is the firefly coming out in game?


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Nikolaevna #5 Posted 19 January 2014 - 03:13 PM

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View Postnotsonooby, on 19 January 2014 - 01:33 PM, said:

Ill repeat the famous question: when is the firefly coming out in game?

 

And I'll repeat the same as usual answer: [not anytime] soon.



notsonooby #6 Posted 19 January 2014 - 04:52 PM

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On a more related topic, so according to the americans, the sherman with the 76mm is more accurate and faster to reload thus the americans consider to firefly to be utterly useless... Well for my two cents with WoT logic:

1. The firefly gun has better penetration right? Considering that the two are from the same era, the fact that the firefly gun is less accurate is quiteunderstandable because   more punch=more recoil

2. Being able to hit a target consistently is nice, but its useless if the round doesn't   penetrate.


Edited by notsonooby, 19 January 2014 - 04:57 PM.

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player1996 #7 Posted 19 January 2014 - 08:09 PM

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I wish this tank EXIST!!!! 

The_Chieftain #8 Posted 20 January 2014 - 02:29 AM

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View Postnotsonooby, on 19 January 2014 - 08:52 AM, said:

On a more related topic, so according to the americans, the sherman with the 76mm is more accurate and faster to reload thus the americans consider to firefly to be utterly useless... Well for my two cents with WoT logic:

1. The firefly gun has better penetration right? Considering that the two are from the same era, the fact that the firefly gun is less accurate is quiteunderstandable because   more punch=more recoil

2. Being able to hit a target consistently is nice, but its useless if the round doesn't   penetrate.

 

That's only part one of the article. There nearly another 20 criteria to go over. I have been told not to make my articles too long and boring, so I split them up.



JarvisXV #9 Posted 20 January 2014 - 02:52 AM

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Much obliged. Looking forward to the next articles.

Just my opinion on the writing style: I understand that it's a technical topic, and it's not really my field, but it's a difficult read. Perhaps, you could add subtitles to make it easier?

 

I hope the Firefly, along with the long-awaited British re-balancing, arrive as soon as possible. I mean, they're already lined-up and just waiting for the go signal, right? :ohmy:



ouchthathurts #10 Posted 20 January 2014 - 03:07 PM

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View Postnotsonooby, on 19 January 2014 - 05:52 PM, said:

On a more related topic, so according to the americans, the sherman with the 76mm is more accurate and faster to reload thus the americans consider to firefly to be utterly useless...

 

1. No, the article said nothing about them considering it to be "utterly useless."

 

2. In most cases, any even slightly nuanced comparison of any two moderately similar guns will not come to a determination that one is "uttterly useless" when the other is not. Such phrases are typically indications of someone who doesn't understand the comparison process at all, or someone who's trying to troll the forums with inflammatory comments.


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rockape79 #11 Posted 20 January 2014 - 07:27 PM

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what I'm waiting for in game (possibly as a rare premium after the firefly) is the experimental 'double barrel' firefly that is supposedly sitting in the australian defence forces military museam, seen photo's of it somewhere, apparently they mounted twin 25pounders that fired similtaniously in a custom turret just to see how much recoil a sherman could handle, before going ahead with the 17 pounders, sort of back on topic, we australians were involved in a lot of armour testing for mother britain

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Mr_Macarthur #12 Posted 21 January 2014 - 08:31 AM

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Odd , I do not see them testing the Armour Piercing Discarding Sabot (APDS)rounds...

or is it perhaps the SVDS rounds....

In any case the 17 pounder was a decent AT gun .It still shared a similar Calibre with its american counterpart .And it had a bit more punch .Even so they were equally ineffective against heavy German armour .Allies still needed a gun powerful enough to engage German heavies at long ranges .America should have just adopted the APDS ammo instead of the HVAP.

And I think the 17 pounder's accuracy problem came from its ammunition ,APDS ammo isn't as accurate when fired from a rifled gun barrel .That is why Modern APFSDS ammo are usually fired by smoothbore guns .

 


Edited by Mr_Macarthur, 21 January 2014 - 10:38 AM.

Any amount of armor can be overcome with a big gun...

DanLBob #13 Posted 21 January 2014 - 08:48 AM

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View Postrockape79, on 20 January 2014 - 07:27 PM, said:

what I'm waiting for in game (possibly as a rare premium after the firefly) is the experimental 'double barrel' firefly that is supposedly sitting in the australian defence forces military museam, seen photo's of it somewhere, apparently they mounted twin 25pounders that fired similtaniously in a custom turret just to see how much recoil a sherman could handle, before going ahead with the 17 pounders, sort of back on topic, we australians were involved in a lot of armour testing for mother britain


That a test model AC.3 Sentinel with the twin 25pdrs. As you say it was to test the recoil forces but the intention was never to fit two 17pdrs in an operational tank. The production AC.3 was to mount the 25pdr but this gun produced less recoil than the 17pdr intended for the AC.4. The simple solution for testing was to install two 25pdrs in a special turret.

 

DanJar



The_Chieftain #14 Posted 26 January 2014 - 02:31 AM

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When we left our brave testers, they were standing out in on a range in Fort Knox in winter (Anyone who's done this knows there are nicer places to be), conducting tests of the M4 with the 17pr gun. With two tests covered, we continue down the list of criteria that the Army Ground Forces Board #2 decided to rate the configuration on.

 

 

Test 3: Flash-back of gun

 

Purpose listed was “To determine the frequency of occurrence and intensity of breech flame (flash-back)

 

The testing process was simple. Every time the gun went “Boom”, the loader watched the breech, and made a note if he saw a flame. No instances were noted when firing APCBC or HE(Reduced Charge), but about 90% of the time, SVDS “Produced a large and rather intense flame at the breech”

 

There were no reported instances of the phenomenon in the 76mm gun, and the 90mm would produce a “large breech flame” in about 60% of rounds fired. Interestingly, the report notes that when firing HVAP with a muzzle brake, there is insufficient recoil on the 90mm to operate the breech, so by the time the loader gets the breech block opened, any flame would have dissipated.

 

 

 

Test 4: Obscuration.

 

This is simple. Once the gun fires, how much obscuration is created?

 

This test was conducted over a two-day period, the ground was wet both days. The bore was measured as 7 feet above the ground (the tank was fired at a forward slope). To conduct the test, a 24” black cross was painted in the centre of a 6x6 panel at 1,000 yards. The gunner, with his x3 sight, and the TC with 7x50 binoculars were given stopwatches. Once the gun was fired, they’d start the stopwatches, and attempt to sense the tracer (For the tracer test). They would stop the stopwatch once they could see the black cross without distortion.

 

 

 

25 rounds of reduced charge HE ammunition and 25 rounds of APCBC were fired in total. The average results were as follows:

 

TC: APCBC 3.4 seconds; HE (Reduced charge) 2.1 seconds

 

Gunner: APCBC 3.5 seconds; HE (Reduced charge) 3.7 seconds.

 

There were additional remarks, though, as those don’t tell the entire story.

 

APCBC Ammunition: The excessive smoke and flash produced by this round makes sensing of the strike by either the tank commander or the gunner virtually impossible at ranges of 1,000 yards or less

 

HE Ammunition: Obscuration produced by this round, although of considerable duration, is not sufficient to obscure the target area and therefore prevent sensing of the burst. There is very little flash and smoke is of a lighter texture than that produced by APCBC.

 

SVDS Ammunition: Observations made during firing of this type of ammunition indicate flash and smoke in excess of that produced by APCBC

 

 

 

The comparative results for 90mm were as follows:

 

TC:  APC 2.2 seconds; HE 1.2 seconds.

 

Gunner: APC: 3.0 seconds, HE 2.6 seconds.

 

However, the report notes that the results for HE are misleading, as there are several factors in favour of the reduced charge HE round: The slower time of flight (1,800 fps vs 2,700), the addition of a tracer on the British round, and the much less intense obscuration caused by having only about half the propellant.

 

The 76mm results for APC were "neglibile" for the TC and 0.8 seconds for the gunner. No records were found for HE firing, interestingly.

 

 

 

Test 5: Blast

 

Purpose was “to determine the blast pattern for the 17-pounder firing APCBC”. It was deemed that there was little purpose in determining the pattern for the reduced charge HE (No full-charge was available) given there was little observed blast from the small propelling charge.

 

 

 

 

The setup for the blast, tracer and obscuration tests. Note the blast meters in the ground.

 

 

 

Without going into great details, you really don’t want to be within 20 feet of the gun, to include at the commander’s hatch. “Prolonged close-range exposure to firing the 17-pounder gun produces considerable discomfort and temporary deafness unless cotton waste or ear plugs are used for protection

 

 

 

The comparative data for the Tank Destroyer Board came from testing of the towed cannon. So although more blast meters were broken by the 90mm than the 17pr, it was pointed out that the cannon was also closer to the ground, which may counter it a bit. No official metering was found for the 76mm, but the troops on site gave personal opinion that the 76mm was less than either of the other two guns.

 

Test 6: Tracer.

 

 

 

The obscuration, blast and tracer tests were all conducted at the same time. On the far left is an observer equipped with a x20 observation device. The TC was using his binoculars and the gunner, of course, his x3 sight.

 

Tracer action in the HE round (reduced charge) was found to be satisfactory, with only infrequent occurrence (Less than 20%) where obscuration was so severe that tracer could not be observed by the crew.

 

 

 

APCBC was a bit more complicated.

 

At ranges of 1,500 yards or less, neither the commander nor the gunner were able to see the tracer because of flash, smoke, and short time of flight to the target. The flank observer 20 feet away was able to see the tracer in about 63% of rounds fired at 1,000 yards range. At 2,000 yards, the commander was able to see the tracer in about 50% of rounds fired, and the gunner 90%. The project officer about 150 yards to the flank indicated a 90% reliability rating, with ignition occurring at 200-300 yards, and burning time sufficiently long to reach some 3,500 to 4,000 yards range.”

 

SVDS was another matter.

 

The tracer element was observed to separate from the core on numerous occasions, and often dropped off on the ground at ranges from 200-600 yards. “ It was theorized that there was some relationship to the sabot separation.

 

 

 

Test 7: Adjustment of Fire.

 

Quoting the report, again.

 

Adjustment problems (Limit, five rounds per target) were fired with APCBC and HE ammunition on panels set up at unmeasured ranges varying from approximately 700 to 2,000 yards.  The method proscribed  in the 17pounder handbook for direct fire up to 2,500 yards was used.” There was no method listed in the manual for adjusting HE.

 

 

 

Results:

 

APCBC: Obscuration was so great and the time of flight so short that neither the tank commander nor the gunner was able to sense strikes except at ranges in the vicinity of 2,000 yards. With the aid of a flank observer located about 25 yards from the tank, adjustment could be made on the shorter range targets, but only at the sacrifice of time."

 

 

 

HE: A total of seven panels were engaged, five were hit.

 

 

 

In comparison, for the other guns:

 

"APC: 76mm APC because of short obscuration time and good tracer is easier to adjust than either 90mm or 17-pounder. Obscuration provided by 17-pounder is greater than that produced by 90mm.

 

 HVAP: No special difficulty was noted in adjusting 76mm or 90mm HVAP.

 

HE: The 17 pounder HE (reduced charge) round is the easiest of all to adjust. With the full charge (2950fps) ammunition which was not available for test, indications are that the obscuration expected will make ease of adjustment comparable to that of the 17 pounder APCBC which was extremely difficult.” The 90mm was given the edge on adjustment to the larger burst provided by the larger HE content.

 

 

 

Test 8. Moving targets.

 

For this test, gunners engaged a 6x6 panel moving at about 8-13mph at ranges from 600-750 yards. Target exposure time was about 50 seconds, during which time the gunner was able to fire three or four rounds. He scored eight hits (including two ricochets) out of 17 rounds. “Observation was such that neither the tank commander nor the gunner were able to sense strikes but had to depend on a flank observer. The low rate of fire was principally due to obscuration and not the ability of the loader to serve the piece.

 

 

 

The 76mm and 90mm guns were making 75% hits in comparable tests. The 76mm had the advantage in rate of fire and low obscuration, allowing the TC to make good use of correction, while the 90mm had a higher muzzle velocity requiring less lead and making tracking easier.

 

 

 

Most of the rest of the tests are actually pretty short and simple, so we'll blow through them in part 3.



Cronium #15 Posted 03 February 2014 - 07:46 PM

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Looking forward to the meat of the article, ie penetration tests.


The_Chieftain #16 Posted 05 February 2014 - 02:35 AM

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This is the third and final part of the look at the US Army's testing of the British 17pr conversion of the M4. If you missed them, these are hyperlinks for Part 1 and Part 2. I'll finish off the report, and then make some observations of my own.

 

Continuing on from where we left off:

 

Test 9. Armor penetration.

Everybody’s favourite.

These were the official ratings in introduction of the report (I’ve done some photo-chopping to make it clearer)

 

The target plate was a 4.5’ x 5.5’ panel 6” thick at 30 degrees fired at 1,050 yards.

APCBC was measured as going through about 7.5” of metal, but SVDS demonstrated a problem. Two impacts were observed on the target. One of the two was sufficiently shallow that it was presumed to have been a ricochet off the ground in front of the target. The other impact happened to superimpose on top of a 76mm HVAP impact, so though it went all the way through, the exact effect could not be determined. After firing 38 rounds SVDS to attain these two impacts, they gave up and went on to do something more productive with their time.

90mm APC/AP was disappointing, with the shells shattering, though it was fired from a 550-round tube with a velocity of under 2,600fps instead of the nominal 2,800fps. The HVAP round, however, punched through not only the armour plate, but also the 1.5” of the hull of the M3 medium behind it against which they had leaned the plate.

 

The page giving the 76mm penetration was missing from the report, but the HVAP impact subsequently superimposed by SVDS was stated as a ‘partial penetration’.

 

  

 

Test 10: Ejection of Empty Brass.

 

Short and sweet, this one.

No instances of failure to eject were ever noticed during firing of the 17-pounder. Similarly, there were no failures recorded in testing for the 76mm. The 90mm also always ejected, unless one happened to be firing HVAP from the muzzle brake version in which case it never ejected.

 

Test 11: Jump firing.

 

Ten rounds APCBC were fired in two-round groups at five aiming marks at a target at 100 yards, with the difference between the two rounds being measured. In the final analysis, the figures were 0.78mil left, 0.15 mil down. For the M4A3(76), the figures were 0.4mil right, 0.9mil down, and for the M26, 0.3mil right, 1.3mil down.

 

The report then goes on to say “Ordnance Department and Service Board firings indicate that jump varies in magnitude and sometimes in direction between tanks of the same model mounting the same gun. Jump data acquired from firing less than ten identical units is considered to be of little significance”. So much for Test 11.

 

Test 12: Operation of elevating and traversing mechanisms.

 

We’re starting to get into less interesting tests here, things will go quickly from this point on as I’ll start skipping a lot of the figures.

Four experienced gunners were brought in to give their opinions of the layouts of the controls of the different tanks. They also measured free play in the mechanisms and the amount of effort required to operate the controls.

 

“The elevating handwheel for the 17-pounder gun is located well forward directly under the gun and is difficult to reach; this results in an uncomfortable, unsteady position for the gunner, especially when he employs turret traverse. This condition is less aggravated when employing power traverse. The traversing controls are located identically to the M4 series and are considered to be satisfactorily accessible”

The 17-pounder turret was rated as in between the 76mm and 90mm tanks in terms of force of effort required, and with the least amount of free play.

 

Test 13: Gun balance.

 

“17 pounder is balanced with the chamber unloaded and counterweight in place. It is approximately 350 inch-pounds out of balance with a round of APCBC in the chamber.

76mm with counterweight is balanced when the chamber is loaded. The 90mm tank gun M3 is approximately 50,000inch-pounds out of balance and requires a coil spring equilibrator to reduce handwheel effort to a usable standard.”

 

Test 14: Turret Torque.

 

The report notes that torque figures can vary between tanks of the same model, and that a comparative test is more or less useless. However, the acceptable torque requirements to move an M4 series turret was established as 200ft/lbs maximum. Measurements of the 17pr turret averaged at about 400ft/lbs on level ground to start the turret moving, and over 1,000 ft/lbs at a 20 degree slope. As a result, the Firefly turret was concluded to be out of balance.

 

Test 15: Power Traverse Response

 

This test was not so much to simply see how quickly the turret traversed, but as to how well the traverse rates responded to a curve determined by the position of the controls. This determines relative ease of power tracking of a target. The Firefly turret ended up in between the M26 (best) and the Oilgear M4 (Worst).

 

Test 17, 18: Firing Switches and Safety.  (Test 16 duplicated 1)

 

A fairly subjective test.

“The toe firing buttons for machinegun and main armament are so located that it is difficult for the gunner to position his foot comfortably. This condition is not serious and the arrangement is probably the most satisfactory possible in a relatively small, basketless turret”, this was considered slightly superior to the standard M4 as it allowed operation of either weapon when engaging in manual mode.

The electrical trigger was the same as on the regular M4.

 

After every loading of the 17pr a “reset” knob has to be operated by the loader in order to close the firing circuit. It functioned well, and added only a fraction of time to the loading process. There is also a mechanical safety operated by the loader, but it requires that he reach across the rear of the breech ring to do so. The 76mm and 90mm mechanical safeties are operated by the gunner.

 

Test 19: Breech Mechanism.

 

The reliability of the breech mechanism for the 17pr was satisfactory, but the assembly/disassembly process was a bit more difficult than on either the 76mm or 90mm guns. The weight of the 17-pounder breech block (123lbs) made it more difficult to handle than either the 90mm’s 102lb block or the 76mm gun’s 41lbs. Further, to remove the breech block for cleaning, the recoil guard must also be dismounted from the 17pr, this was considered a design deficiency.

 

Test 20: Recoil mechanism.

 

In terms of operational effectiveness, no difference was found between the three mechanisms. The 17pr was a little more difficult to service, but the additional tool and task was considered a minor issue in the larger scheme of things.

 

Test 21: Loader’s Hatch.

 

“The loader’s hatches on Medium Tank M26 and Medium tank M4A3 are considered to be more desirable because of simpler construction, spring loading (against closing) which aids in opening, and in an open position the hatch cover is almost flush with the turret top”

 

Overview.

 

At the end of the report, they provide a tabulated page of rankings by criterion.

 

 

The recommendations of the report were as follows:

“a. The 17-pounder tank gun Mk VII and Turret Assembly be considered generally inferior to like components of Medium Tank M26 (90mm Gun M3) and Medium Tank M4A3 (76mm Gun M1A2)

 

b. The British 17-pounder tank gun Mk VII and the German 75mm Gun KWK-42 be made the subject of further study by qualified gun design personnel and the desireable features of both weapons be considered in the design of a superior gun for use in the development medium tank”

 

Chieftain's Personal Commentary

 

So as far as both Ordnance and Army Ground Forces (Armoured Force and Tank Destroyer Board both partook in the Fort Knox tests) were concerned, their staying with the M4(76) instead of buying/building Firefly was justified. But the ultimate test is the battlefield, were they correct if that is brought into play?

 

I submit that there is an argument that yes, in practice it was the correct decision as well. The bottom line question is “What could the 17pr Sherman Firefly do that the 76mm M4 could not do at least as well, if not better?” The answer is basically nothing. Both tanks were more than capable of reliably dealing with Panzers, StuGs and Tigers from all angles and at reasonable ranges. Neither tank had much of a hope against King Tigers from the front, both had no difficulty from the side.  As the tests at Isigny showed, neither could reliably penetrate the front of a Panther, except at close range. There was perhaps a narrow band from at closer range where 17pr had a more reasonable expectation of killing Panther, while the 76mm was being a bit optimistic (The short range band at maybe 400-500m where SVDS might still actually go in the direction you were aiming while 76mm was of questionable penetration), if you came around the corner and had to get a round off quickly enough that you didn't have time to aim for the turret. In pretty much every other factor of tanking, the 76mm M4 was the superior tank. It could engage targets more quickly, it could put more explosives on targets in a shorter amount of time, it was more accurate, it had safer ammunition stowage, kept the 5th man and bow MG (if you consider that as a good thing, which in WWII it seems to have been), was more comfortable…

 

But did the British share this assessment? Xlucine on the NA forum was doing a bit of digging in the British archives, and one of the documents he dug up had this table in it.

 

At first blush, it seems to give a good nod to the 17pr. It's good enough to punch through Panther's lower glacis at about 2km, while the 76mm has to get to under half that distance. HVAP can't go through the front slope at all by British standards, while SVDS will do it at a kilometer. (This assessment seem to be at variance with the Isigny tests which gave at least a chance to HVAP) 

 

Good to know. Also, in practice irrelevant. I go back to the accuracy report the British put out that I referenced in US Guns German Armor Part 1.

 

At the range to which the 76mm must close in order to go through the Panther's lower glacis, SVDS is rated at about 14% chance to hit a 5'x2'target. The same report gives 76mm APC (Reputedly not as accurate as HVAP) a 96% chance to hit the same sized target, which also happens to be about the size of the turret. Which the 76mm tank may as well aim for instead at a longer range anyway. Where is the practical advantage to the capability to puch through at extended range if you can't get the shell to hit to begin with? By the time Firefly gets close enough to hit the target, 76mm would be punching through as well anyway.

 

 

So why does Firefly get all the glory and positive reputation as 'Best Sherman'?

 

I suggest that it’s for the simple reason that it was there, and in numbers. The real advantage that Firefly had was not that the tank was better, but it was that the British Army had decided to implement it in substantial numbers before the invasion of Normandy. A number of 76mm tanks were sitting in the UK during D-Day, and HVAP was not yet in production. American commanders simply did not think they particularly needed it. Why add extra ammunition to the logistical tail of the battalion? Why make a bunch of expensive HVAP ammo when the standard AP was good enough?

 

These assumptions that the Americans had were simply wrong. It was not the fault of the tank, or the people who had developed the tank and ammunition in time to partake in the Normandy invasion. It’s not to say that Firefly doesn’t deserve its reputation, but arguably it does not deserve it as being a better tank than the 76mm M4, and the US forces are equally arguably given an undeserved hit for not choosing the tank themselves, beyond the 81 they had converted. (Possibly as much due to political pressure as anything else).

 

These were policy decisions. Remember that the decision had been made to build nothing but 76mm tanks starting 6 months before D-Day, but was not shipped over quickly enough. HVAP could have been built in greater numbers earlier, but absent a perceived need, the ammunition was given a lower priority for the raw materials. 76mm was a great tank. It just was never given the same opportunity to prove it.




amade #17 Posted 05 February 2014 - 03:01 AM

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So in short WoT Logic =/= RL Logic.

 

Like everybody else I'd go for the 17pdr in game but I can understand why the US felt the 76mm was adequate.



karl0ssus1 #18 Posted 05 February 2014 - 08:51 AM

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View Postamade, on 05 February 2014 - 08:01 AM, said:

So in short WoT Logic =/= RL Logic.

 

Like everybody else I'd go for the 17pdr in game but I can understand why the US felt the 76mm was adequate.

I dunno, I like its capabilities in the church series, what with the accuracy, pen and ROFl, but after reading this, its pretty clear that that doesnt translate over to the sherman.

If WG sticks to attempting historicity, then the 76mm might be the better option for the listed reasons. Then again, they might not, have to wait and see.

 

Could be a long wait though? This year? Next year?


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amade #19 Posted 05 February 2014 - 09:30 AM

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I wasn't commenting on why WG didn't include the Firefly in particular, I was just commenting on why things were the way they were in WWII. When it comes to historical accuracy for the game it takes a back seat to gameplay, in which case I doubt the reason WG hasn't decided to put it in game yet is because the US historically thought the 76mm was adequate for their needs. Whatever the obstacle is most likely gameplay related. That said, I'm pretty sure WG still takes into account of all the stuff that they research when it comes to balancing the tanks in game (like the results from the obscuration tests may be the basis of why WG decide certain guns have should certain aiming times, etc).


karl0ssus1 #20 Posted 05 February 2014 - 12:12 PM

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I wasnt really commenting on that either. IIRC, the wait is because WG dont want to introduce it as a premium, and theyve been having a little trouble researching the second Brit med line.

My main point was that yeah, 17 pounder sherman may not be as awesome as 17 pounder church (in terms of gun stats), and the 76mm could remain a viable choice.


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