Why does the M10/M18 have no roof?

[Rifle1860]

I am plagued by the question and I would love to get the real answer.

Most of the German Tank Destroyers have no turret. I understand that this was done because

- they were cheaper to produce and used less metal;

- they are easier to maintain (no turret ring etc.)

- They were faster to produce

- They have a lower profile (harder to see and hit)

- they took advantage of thicker frontal armour

The list goes on.

But why did the US take the M10/M18 approach? In several games recently, I have lost M18s to mortar fire. This must have been a real issue.

My initial thoughts are:

- There may have been an "overpressure" problem with an enclosed turret with the larger guns;

- The crews may have been able to see and hear more from an open turret;

- The US had a different doctrinal approach to Tank Destroyers (most likely case)

The US certainly did not have some of the indistrial and material limitations the Germans did.

Any thoughts?

[Vergeltungswaffe]

For the German, non-turreted TD's, all your reasoning is sound except the lower silhouette. That was a nice by-product, not a desired effect.

Somewhat similiar to Soviet era tanks being small. Many think the autoloader and low silhouette was a tactical design, when in fact it was also a by-product of the need for strategic resources when building many thousand's of them, with the least possible materials and at the lowest possible cost.

As to your question, I don't know about the first statement. Overpressure *might* have been a factor, but your 2nd and 3rd statements hit the nail on the head. US TD doctrine called for the best possible spotting and shortest possible engagement time. Open turrets were reckoned to be the way to do that, at the time. Of course, after WWII, there were no open topped AFV's produced, other than AA and Arty vehicles, so the lack of protection must have been too much for the types to continue.

[Cathedral]

Another added bonus of an open roof TD was the ability to perform various task quicker. After standing inside different open roof TD's at Aberdeen, I can attest to this. Imagine what is quicker to resupply with thirty new AP rounds, an open top TD or a traditional tank. Also, reloading an open roof TD would be quicker, as there is more room to maneuver, toss shell casings over the side, etc. On a side note, I would think that an open top TD would be much less hot, cramped, and noisy than a traditionally built TD.

[PJungnitsch]

<blockquote>quote:</font><hr>For the German, non-turreted TD's, all your reasoning is sound except the lower silhouette. That was a nice by-product, not a desired effect<hr></blockquote>

In the original Stug development contract the main specification was for a low silouette ('ideally, no higher than a man' was what it stated, AFAIK). This ruled out the use of a turret.

In combat, the low silouette was felt to give tremendous benefit, especially as the drivers were trained to take advantage of terrain.

The ease of construction and the ability to upgun otherwise obsolete chassis with a more potent gun than could be fitted into a turret were all additional advantages that were especially important with the manufacturing constraints the Germans were under late in the war.

[Cathedral]

You're plagued by questions regarding open roofed TDs? Relax, really. It isn't a question that should plague you.

[Redwolf]

Several sources also state that the M10/M18 turret was manned by one man more, two loaders, one gunner, one commander. Two loaders make for a higher rate of fire, besides robustness against exhaustion and injury, but need more space.

As for the roof, I think the real question is, "why does a real tank have a roof"?

Artillery. A real tank is suposed to exploit breakage of enemy lines to drive through them and do nastly things behind them. It is a requirement that this vehicles is somewhat resistent against artillery, especially artillery that can retarget quickly like mortars or against directly firing mortars. Also they would come near enough to enemy infantry to get grenades thrown into an open turret (not voluntarily, of course, but still).

The tank destroyer on the other hand is supposed to operate within the protection of the own lines, where there is fewer observation from enemy artillery, more pressing targets for enemy artillery anyway, and no enemy infantry in grenade-throwing distance.

To put it differently, if you want serious MGs on your AFVs, you also want a roof

[Blackhorse]

lighter weight, hence faster speed...or so the theory went.

[Rifle1860]

<blockquote>quote:</font><hr>Originally posted by Cathedral:

You're plagued by questions regarding open roofed TDs? Relax, really. It isn't a question that should plague you. <hr></blockquote>

OK, so I don't have much of a life and am easily "plagued". In recent days, I have played 2 or 3 QBs with a friend of mine. I select Armd ME as the type. Each time, the US gets a bunch of M18s and the Ger get a bunch of Hetzers. So, the Hetzers move and blow up real good (they are great if left static) and the M18s get some arty on them - same effect.

This triggered the question. Obviously, US and German had diffrent doctrine that drove the veh design. This is assuming the perfect state where it is not the vehicle availability that drove the doctrine. The more I think about it, it seems that US TD design was driven by the characteristics of Speed (veh and turret speed), Firepower and Manouvre. Germany seems to have embraced Protection (low profile, thick front, closed top) and Firepower.

In fact, it appears to me that the US saw TD's as offensive weapons and the Germans more in a static or defensive role.

Just a rambling thought.

Over

[Slapdragon]

The US Tds were designed to counter major armored offensives as mobile AT guns which could rapidly move to and seal off break throughs of the main line. Thus mobility and rate of fire was seen as needed, along with hitting power of the weapon, but it was never really designed to fight on the tactical offensive. In fact they were used that way often. US TDs really are powerful units. The M10 not so much as the M18 and M36, and the one time they face a real breakthrough, in Bulge, they performed just as they were suppose to, but the US was stuck on the attack and the Germans really did not have the strength to mount major operations on any front by 1944.

The combination of open top, 2 loaders, and light weight ammunition makes the M18 one of the fastest firing tanks in the ETO. Oral histories say crew in practice could fire 20 rounds in a 1-minute burst, with a 15 round 1 minute barrage being more normal in combat. M18 tactics called for it to either lay in wait for leapfrog to the flanks of enemy armor. When the heavier armor was engaged M18s would fire one or two rounds from a full stop, then start firing on the move (around 15mph cross country), relying on quantity rather than pure accuracy to keep them alive to keep them alive. If it seemed they were getting bracketed, they would take off to 30 mph and retreat. The M18 was never really used to take or hold ground, it was used as a hunter.

The M10 was often used as just another infantry support weapon, and paid a heavy price. It was used much like a M4, in the company of infantry.

The M36 was used like fireflies, for long range gunnery out of the range of infantry weapons.

[Redwolf]

<blockquote>quote:</font><hr>Originally posted by Rifle1860:

In fact, it appears to me that the US saw TD's as offensive weapons and the Germans more in a static or defensive role.

<hr></blockquote>

I don't think that is the case. The U.S. TD were clearly intended to drive around behind their own lines and check enemy breakthroughs or possible breakthroughs. Same for the Germans.

However, there is a difference in that late-war Germany gave its (real) tanks better anti-tank capability and that at that time they were more on the defensive as a whole, that they had more of the AT-capable tanks behind their lines instead of driving around in enemy hinterland (or busy trying to do that).

I think it is a good explanation that the U.S. gave their infantry lines initially very few TDs and then rushed larger formations from further behind to the scene of an actual threat.

Whereas the Germans gave lots of StuGs and Jagdpanzer (but no heavies like Jagdpanther) to the front-line formations (besides their organic Marders and Hetzers), so that these were more scattered than U.S. TDs and hence would play not a very big role in a serious battle. However, the Germans had tank formations with good AT capability behind their lines that they could send to scenes of actual large-scale armour attacks. A Sherman battalion would be less useful for that.

Also, the Germans had the heavy tank destroyer battalions that they could send as a second, really massed and really deadly reserve.

Has nothing to do with roofs, as I think the roof question is not releated to a more or less agreesive doctrine for the vehicles. A Jagdpanzer still sucks when driving into enemy lines, roof or not.

[John Kettler]

Rifle1860,

You forgot the M-36!

Aside from the various issues identified by the other posters, there's one they missed: the ability to get the TD hulldown on slopes much steeper than

tanks could. This is because the inside of the turret roof inherently limits gun depression. One can't, after all, have the recoiling breech slamming into the underside of the turret top. If the gun mount has no roof, though, it is possible to exploit the full depression capabilities of the gun without having to expose all or most of the hull in order to shoot down from steeper hills and ridges.

If BTS does its job right, most Russian armor will suffer in this regard in CMBB. Those low profiles translate into squashed turrets and fighting compartments for most tanks and fully enclosed SU type vehicles, resulting directly in serious reduction in depression limits. This should translate directly into increased vehicle exposure when firing downhill in significantly elevated terrain. It was still an issue back in my days (1978-1989) as a Soviet Threat Analyst and is still a problem now. Their AFVs are designed for the steppes.

Hope this helps.

Regards,

John Kettler

[ 10-24-2001: Message edited by: John Kettler ]</p>

[Iron Chef Sakai]

<blockquote>quote:</font><hr>Originally posted by Rifle1860:

I am plagued by the question and I would love to get the real answer.

Most of the German Tank Destroyers have no turret. I understand that this was done because

- they were cheaper to produce and used less metal;

- they are easier to maintain (no turret ring etc.)

- They were faster to produce

- They have a lower profile (harder to see and hit)

- they took advantage of thicker frontal armour

The list goes on.

But why did the US take the M10/M18 approach? In several games recently, I have lost M18s to mortar fire. This must have been a real issue.

My initial thoughts are:

- There may have been an "overpressure" problem with an enclosed turret with the larger guns;

- The crews may have been able to see and hear more from an open turret;

- The US had a different doctrinal approach to Tank Destroyers (most likely case)

The US certainly did not have some of the indistrial and material limitations the Germans did.

Any thoughts?<hr></blockquote>well. for one blame our tank engineers, but 2nd, the american army was able to mass produce at such high numbers because our equipment was made simple and cost effective. our stuff was far from top quality, but our output was impressive. the german heavy tanks, though superior, too much longer to produce, though their td's were produced reltivly fast. we also did not share the same outlook as germany in ground warfare. we like britain and mostly france, wich we modeled our army after in the 30's and up till the country fell swiftly, viewed armor as soley an infantry support weapon, not to be used en mass, ect....basicaly the germans needed the right tools for their strategy, wich they made. the us tank destroyers were actualy an adjustment made from our tanks, not unlike the rhino. we made a fast adjustment and in come the m-10's. the british were not too keen in tank design as well. the french b1 bis was very mpressive for it's time, but the only allied country that was adept with tank design was the soviet union. though the design was actualy made by an american, for the T34's. the whole suspension, sloped armor, and wide tracks were designed by Christie, hence the christie suspension used on the russian bt series tanks and t-34's. our military did not want to pay him for his design so he sold it to the soviets in the early 30's i believe

[Triumvir]

Iron Chef Sakai, your name is B1FF and I claim my two-fifty.

[Iron Chef Sakai]

who is biff? i don't get it

[russellmz]

the best explanation i ever got: (of course i like stuff with an edge not directed at me)

<blockquote>quote:</font><hr>

Basically, a bunch of non-brilliant US Army generals came up with this plan. They figured that the rest of the world was fighting the war all wrong. Despite the fact the the Brits, Germans, and Soviets had been fighting for several years, and all were moving towards the multi-purpose medium battle tank, these particular US Army dolts knew better than everyone else how war should, would, and could be fought.

See, tanks were not meant to fight other tanks. Tanks were meant to support infantry. To support infantry, you had to go get close to them, so yout infantry support tank had better be closed top. But, since your tank will never fight other tanks, it was a waste of resources to put a gun in it that could engage other tanks. Result: the 75mm armed M4 Ronson.

Now, the job of destroying enemy tanks was going to be done by AT guns. Problem is that unless your opponent is dumb enough to always walk into your AT screen, the bad guys tend to be somewhere where your towed AT guns are not. So you had to mount them on a vehicle. Not a tank, mind you, 'cause tanks are only for infantry support and exploitation.

But this mobile AT gun (dubbed the tank-destroyer) certainly would not need heavy armor or even a top, since it would never get itself into a position where it would be attacked by enemy infantry, oh gosh no! All it needed was a decent gun and good mobility.

So we got the M10 TD. Of course, the result of all this was that the US ended up with a tank that got wiped when it had to go up against other tanks, which happened a lot since apparently someone forgot to tell those pesky Germans that you were not supposed to fight tanks with tanks. And we got a TD that was not real effective against other tanks, because it did not have the armor or gun to trade shots with the very vehicles it was designed to destroy. But we biult 'em by the tens of thousands, and the Germans destroyed them by the hundreds, and we won despite the spectacular idiocy of US Army procurement.

The later equipping of Shermans with the 76, and the advent of the 90mm armed M36 and the rather belated appearance of the M26 Pershing Medium tank were all after the fact attempts to fix McNairs stupid error. The scary thing is that even those stop-gap measures may not have happened as quickly as they did if a short bomb drop from an American plane hadn't killed McNair. While American privates were getting blown away at an alarming rate in Normandy because of inadequate armor, McNair was still insisting that the 76mm Sherman and 90mm TD were unecessary. That bombadier should get a medal.

Jeff Heidman

<hr></blockquote>

[rexford]

German StuG and other self-propelled vehicles had no turret because it was the only way to get a bigger gun on a tank chassis that would otherwise have too small a turret ring.

PzKpfw III tank could not accept a 75L43 or L48 gun, PzkPfw IV could not accept 75L70 or 88L56, PzKpfw II could not accept 76.2L51.5, PzKpfw 38t could not handle a 75L48 in a turret.

M10 were supposed to defend against marauding German tanks, and emphasis would be on seeing and firing on attackers. Rate of fire probably is higher in open top unless it is raining or snowing.

There have been posts where Sherman air intake was through commander hatch, so snow would be drawn into tank interior along with cold air. Theory was that in North Africa air intake from outside would help cool things inside vehicle.

Wonder if M10 also drew air downwards into hull through open turret?

Previous posts by Jeff Duquette indicated that tank engagements tended to be short lived affairs, where one side or the other would quickly disengage after suffering losses and total force annihilation was usually rare (U.S. experience, not so on Russian front). So M10 with open top would be used in limited time frame combat, get to breakthrough or go into action against defensive position, blast away and then get out before artillery zeroes in.

Regarding StuG profile, Michael Wittmann was able to knockout T34 with the 75L24 gun on StuG IIIA using one shot per tank, by taking advantage of low profile and those scissor periscopes.

The StuG would hide in total concealment and look over the LOS obstacle using the scissors scope, where the commander and gunner both had them. So when the StuG was ready to jump out and surprise the T34's it had every thing sighted with low risk.

Wittmann took out the T34's by hitting the turret ring.

The scissors scopes aided alot due to other factors, higher magnification and light gathering qualities than normal sights in PzKpfw IV, and binocular vision allowed greater accuracy in estimating target range.

Regarding German SPG profile, the armor on those vehicles was often shoddy, like Marder, StuG III with 50mm plates and Nashorn, which meant that they either were used at long range where return fire was not expected to be too accurate (or SPG would back away once return fire became too accurate), or small/low profile would take advantage of low cover and reduce enemy hit probability.

In terms of accuracy, a low profile is more important than a narror width.

[JasonC]

American AFV thinking was a year and a half behind Germany's because the US entered the war a year and a half after the fall of France, which saw the first serious fights with armor on both sides. The Germans went through the same stages, they just went through them earlier. The M10 is a Marder with a turret, and the M36 is a Nashorn (wannabe, anyway) with a turret. The Germans were still making 75L24 tanks in early 1943, and the US was still using short 75 tanks in late 44. The US upgunned to 76mm tanks a year and a half after the Germans had upgunned their fleet to 75 long. If the war had gone on another year the US would have fielded upgunned and uparmored Pershings, which are roughly equivalent to Panthers (in weight, armor protection, gun).

The Germans upgunned their TD units faster than their main battle tanks because they had the same doctrine about PAK fronts to defeat armor and tanks used en masse for exploitation. They had the same delays and foul ups, from quartermasters trying to keep the 37mm because they already had the ammo, to exploitation theory tankers insisting the 50L60 was unnecessary because tanks didn't fight tanks, so a 50L42 would do. They waited 9 months from the time they fitted the long 75 to the Pz III chassis (long StuG in mid 1942) before abandoning the turreted version (75L24 late Pz IIIs in 1943). They just started having their screw ups at Sedan in May of 1940, so by May of 1943 they had pretty well gotten over all of them. By December 7, 1945, the US would have pretty well gotten over its design and doctrinal screw ups too.

[JunoReactor]

Dont forget the American love for convertibles!

[Richard Morgan]

Iron Chef Sakai

You don't perchance know anyone called Lewis (aka Username)who used to be a member of this forum - or are you Lewis under a new handle??

Just interested,

Richard.

[Patgod]

<blockquote>quote:</font><hr>Originally posted by JunoReactor:

Dont forget the American love for convertibles! <hr></blockquote>

well yeah, i mean you cant pick up chicks in a SHERMAN. they dont even have a sunroof. well ok they do, but only after a panther gets ahold of one

speaking of which, if you REALLY want to get the girls you gotta have a panther, or a tirger. they draw women like fireflys

oh yes, pun intended(its 1:30am cut me slack)

[Vanir Ausf B]

<blockquote>quote:</font><hr>Originally posted by John Kettler:

If BTS does its job right, most Russian armor will suffer in this regard in CMBB. <hr></blockquote>

Alas, it will not be so. Modeling of different gun depression for various vehicles will not be in CM2. At least that was the last word I heard. It has something to do with the way the game engine calculates hull down status. I can't remember the details.

Anyway, Tero will have a fit when he finds out. I anticipate many long threads

[Tero]

Originally posted by Vanir Ausf B:

Anyway, Tero will have a fit when he finds out. I anticipate many long threads

Now, where did I put that paper bag again. I better stock up before I run out of them later on.

Thanks for the heads up. Can't say I am surprised.

[Cpl Carrot]

I always thought the reason was due to a rich diet of beans......

[Wreck]

I am surprised nobody has mentioned air superiority yet. The Allies had it, so they did not have to worry about losing open topped AFVs to strafing. The Germans didn't, and did.

Similarly the Allies has far more artillery, so that the risk of being behind the lines out of sight but in arty range was not very great. The risk for Germans similarly situated would be considerably higher.

The threat environment has a big effect on the vehicle fleet, for two related reasons. One is, because things that can easily be killed will be, thereby lowering their representation in the fleet disproportionately. But also the fact that a design is exceedingly vulnerable to some common enemy weapon is much more easily grasped in the rear, among the decision makers who will get the design changed or obsoleted.

[Redwolf]

<blockquote>quote:</font><hr>Originally posted by Wreck:

I am surprised nobody has mentioned air superiority yet. The Allies had it, so they did not have to worry about losing open topped AFVs to strafing. The Germans didn't, and did.

Similarly the Allies has far more artillery, so that the risk of being behind the lines out of sight but in arty range was not very great. The risk for Germans similarly situated would be considerably higher.

<hr></blockquote>

Uhm, Wreck, I don't think that matches with the timeline. At the time the M10 has been designed (or the specifications with the open turret had been set), the Amercians couldn't know that they would have that much air superiority.

For the Germans, I can agree that at the time they switched the Marders to the Hetzers and they designed the Jagdpanzer IV, they could expect air and arty inferiority. But the key point in time is IMHO when the StuG's requirements were switched to include a closed roof. At that time, the Germans surely didn't admit they would not have a chance in the air soon.

<blockquote>quote:</font><hr>

The threat environment has a big effect on the vehicle fleet, for two related reasons. One is, because things that can easily be killed will be, thereby lowering their representation in the fleet disproportionately. But also the fact that a design is exceedingly vulnerable to some common enemy weapon is much more easily grasped in the rear, among the decision makers who will get the design changed or obsoleted.[/QB]<hr></blockquote>

No doubt here. All that thin-armour and open-top crap didn't turn out useful in the end, tough vehicles were what mattered, and they were worth the cost. But I don't think the air issue can serve as an explanation for the open-turret U.S. tank destroyers and the closed StuG.

I really like the bean explanation