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Open-topped WW2 Armour - what was the rationale?

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julianj

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I was just mulling over WW2 and its plethora of open-topped armoured vehicles. For example the M10/M36 Tank Destroyers. The open top must be good for situational awareness, but with the downside of being unpleasant for the crew a lot of the time. I can understand the design decision on a lot of the improvised vehicles, e.g. the Marders, for space/weight reasons, and halftracks because the crew need to debus quickly, but that still leaves me with a question over purpose-built equipment like the M10. Even in 1941 the open-top would be vulnerable to shrapnel, air attack and snipers, although these would not be so prevalent as later in the war. On the plus side, you can get out quickly. I was at a military fair a few years ago with Shermans, Cromwells and the like...I had felt my skinny earlier teenage self would have had difficulty getting through those hatches, let alone if it was burning...

You can see it would be "brass monkey weather" for those poor sods in the picture.

As an aside, I just noticed (again) that the M10 doesn't have a co-ax MG, which is another inexplicable omission.

What are your thoughts? Why did US TD Command (or the Ordnance Board) take this decision? It would have added a small amount of cost, weight and complexity to the manufacture, but not that much.
 

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I can see positives - for example reloading ammo, or "bombing up" as the British would say - I'm sure that is easier with an open topped compartment. It's just that inconvenience doesn't quite rack up against getting your head blown off. I'm fairly sure some of these served in the Pacific theatre which must have had such problems.
 
So far as I understand it the main reason was a better view. The original doctrine said the tank destroyers should be used in ambushes and as second line. Frontal or open fighting against tanks wasn´t the original task. The doctrine coninued that tank destroyers should use their speed and prepared ambush positions instead of armour to knock out tanks. Furthermore, and as You already mentioned, the reloading was quicker/faster since there wasn´t a crampy room the loader had to deal with. So an open turret was seen as fitting enough.

Greetings
 
Thanks @Sempai I agree with what you say, it's just reality doesn't quite match the theory - for example we have seen film of M10s used as close infantry support in towns, which I'm sure is not doctrine. The more I think about it, it was an artillery viewpoint rather than an armour one.
 
Much of that what was thought fitting crushed under the weight of the reality if the real combat broke out. And many a unit wasn´t used as it was thought but how the situation demanded then. So if I have to decide if I get into battle with a M10 to support my infantry or not - I always will take the M10 - even if it gets destroyed early in the battle. And the Germans can sing a song of what was thought fitting until the situation during Barbarossa showed it wasn´t fitting. But it was still better as to do without any assistance. I think for example on the use of french tracked vehicles to carry a german PaK - called "Marder" tankhunter.

Greetings
 
Like a tennis match TD's stay on the baseline and tanks go for the net. TD's as mobile AT guns stops enemy breakthroughs.
 
I was taught that when you come to a knife fight with a pen, use the pen. Its may not be what it was designed for, but it will do in a pinch. In combat you use the tools at hand to get the job done, even if it means putting the square peg in the round hole. Proved it works when I was a kid, just needed a hammer!
 
I also believe the open turret allowed bigger guns to fit in turrets and chassis that wouldn't otherwise be able to fit them, like a 90mm on a Sherman.
 
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burning_phoneix said:
I also believe the open turret allowed bigger guns to fit in turrets and chassis that wouldn't otherwise be able to fit them, like a 90mm on a Sherman.
Click to expand...
They were ATG's and you need to be situational aware with these systems. Traditional ATG's quickly became obsolete after WW2. Once you fire you need to get out in minutes you can expect mortars or anything else. AT's on TD's are meant to stop counter-attacks and need to be mobile. Even the 155 mm was mounted on a Sherman Chassis.
 
julianj said:
I was just mulling over WW2 and its plethora of open-topped armoured vehicles. For example the M10/M36 Tank Destroyers. The open top must be good for situational awareness, but with the downside of being unpleasant for the crew a lot of the time. I can understand the design decision on a lot of the improvised vehicles, e.g. the Marders, for space/weight reasons, and halftracks because the crew need to debus quickly, but that still leaves me with a question over purpose-built equipment like the M10. Even in 1941 the open-top would be vulnerable to shrapnel, air attack and snipers, although these would not be so prevalent as later in the war. On the plus side, you can get out quickly. I was at a military fair a few years ago with Shermans, Cromwells and the like...I had felt my skinny earlier teenage self would have had difficulty getting through those hatches, let alone if it was burning...

You can see it would be "brass monkey weather" for those poor sods in the picture.

As an aside, I just noticed (again) that the M10 doesn't have a co-ax MG, which is another inexplicable omission.

What are your thoughts? Why did US TD Command (or the Ordnance Board) take this decision? It would have added a small amount of cost, weight and complexity to the manufacture, but not that much.
Click to expand...
TDs are AT Guns and not tanks. They may have been used as tanks, but it was not their purpose. Tanks can be used as TD's, but it is not its primary purpose. Its evolution was the MBT. TD's need to be mobile they can guess but don't know where the counterattack comes from. TD's Have an AT Gun and designated munitions. For example, the Hellcat 76 mm and HVAP ammunition, Easy Eight Sherman the same 76 mm gun but no HVAP ammunition. Yes, after WW 2 they realized train crew for long-range AT gunnery better engines and optics, and they can be used as a TD. The MBT became into being and TDs were in the history books.
 
ChuckDyke said:
They were ATG's and you need to be situational aware with these systems. Traditional ATG's quickly became obsolete after WW2. Once you fire you need to get out in minutes you can expect mortars or anything else. AT's on TD's are meant to stop counter-attacks and need to be mobile. Even the 155 mm was mounted on a Sherman Chassis.
Click to expand...
When was the 155mm mounted on a sherman? The M40 GMC?
 
burning_phoneix said:
When was the 155mm mounted on a sherman? The M40 GMC?
Click to expand...
Yes, it was mounted on a Sherman Tank Chassis.
Long-Tom.jpg
 
julianj said:
Thanks @Sempai I agree with what you say, it's just reality doesn't quite match the theory - for example we have seen film of M10s used as close infantry support in towns, which I'm sure is not doctrine. The more I think about it, it was an artillery viewpoint rather than an armour one.
Click to expand...
TD's were used for anything and everything.. The only time the TD's were used as per their doctrine to stop an armored attack was in North Africa. TD's were used "as tanks", in infantry support, and as indirect fire weapons. I believe in "The Chieftain's" Think Tank series of videos one of the experts stated that TD's fired more HE in indirect fire roles than any other type of ammo.
 
Only 100 M-12s were built in 1942 for use in World War II. A French First World War era 155mm gun was placed on a modified Grant chassis. Typically the US Army Ground Forces did not see the need for a 155mm self-propelled gun at the time, so the M-12 was not put into large scale production. When they did see combat in Normandy, they were invaluable not only for indirect fire, but also for destroying pillboxes and heavy German tanks with direct fire.
 
burning_phoneix said:
Yes, that is my point: Such large weapons needed open topped turrets or no turrets at all to fit on the chassis.
Click to expand...
Elevation of the gun too, indirect fire is the role of artillery. The functions overlap. We can construct an earthen ramp to give a tank the elevation for indirect fire missions. It depends on the command. Guderian was short of armour so he requested Stug III's to make up the number.
 
Thanks to everyone for their posts. I particularly liked The Chieftain's video (H/T @ChuckDyke) which I hadn't seen , which really does give a tremendous insight into the way the thinking evolved from just post WW1 to the end of WW2. Loved the sly humour, e.g.a US official called General Twaddle LOL (non-English speakers check your dictionary!).
 
Regarding US tank destroyers I believe overall vehicle weight was also a consideration in the open-top design, along with visibility and ease of re-loading.. American TD doctrine imagined the TD would dash around from concealed shooting position to shooting position, so keeping the vehicle as light as possible was a deliberate design feature. The paper-thin armor also helped keep weight down and improved mobility.
 
They were self-propelled ATG's. Compare them with TOW and other ATGM on IFV's today. They were used sometimes as tanks but it was not their primary purpose. ATG was too heavy to be deployed quickly if they were limbered behind a truck. Once they gave their positions away, they were sitting ducks not so the TD. Destroy a tank and swiftly reposition the vehicle. Even the Gunship today can be regarded as a modern TD.
 
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