Driver Hatch Thickness on T34 and T34/85

[rexford]

Several forums in the past have posted e-mails indicating that the subject tanks had 75mm thick driver hatches.

Looking at a photo on the Russian Battlefield site at

http://www.battlefield.ru/t34_76_2.html

which is entitled "The new T-34-76 Model 1942 leaving the "Krasnoye Sormovo" Factory.", one can measure the approximate observed thickness of the gun barrel opening (76.2mm) and the open driver hatch edge thickness.

Using a ruler and measuring against the photo, the driver hatch edge thickness appears to be 80% as thick as the gun barrel inner diameter (76.2mm) on the T34 Model 1942. Measured 5/50 of an inch across the barrel opening and 4/50 of an inch for the driver hatch thickness.

The drawing at the top of the web site page results in about the same relationship. While the edge of the driver hatch appears to be about 61mm thick, it is possible that the 61mm edge might suddenly or gradually taper down to 45mm in the center areas (where the edge thickness was to beef up an area that is vulnerable to edge effects).

Are there any design or production drawings out there that give a definitive driver hatch thickness?

[ November 21, 2003, 05:45 PM: Message edited by: rexford ]

[rexford]

A cross-sectional drawing on the following site (picture 2) suggests that the driver hatch was thicker than the 45mm glacis by about one-third, based on scaling;

http://afvinteriors.hobbyvista.com/t34/t34a.html

[ November 21, 2003, 05:37 PM: Message edited by: rexford ]

[Sardaukar]

Would that indicate that it's not a weak spot ? My first instinct says it doesn't depend so much about thickness, but arragement. But it indicates that Soviets were aware of possible weak spot.

Cheers,

M.S.

[rexford]

If the T34 driver hatch is 60mm thick, a 75mm APCBC hit on the center of the hatch would be resisted by an effective thickness of 144mm (quality of 1.00), which would defeat all 75mm L43 and 75mm L48 hits at any range.

[Sardaukar]

Any idea if hit could break the whole hatch out of it's "hinges", so to speak ? That would render thickness relatively unimportant. Unlikely event, if correctly designed, but intriguing possibility.

Cheers,

M.S.

[Sergei]

Or maybe there were some early models with hatch doors designed to open inwards...

[gunnergoz]

Originally posted by Sergei:

Or maybe there were some early models with hatch doors designed to open inwards...

A joke, right Sergei?

Actually, doesn't anyone have easy access to a real T-34 for a reality check? There are a lot of them around on display and quite a few in private hands. That's what I'd use for reference, not some photos...Why guesstimate when we still have the real article to go by?

Just my 2 bits.

[Holman]

Good lord... they have hatch grogs even!

[rexford]

Jeff Duquette posted some great photo's and info on the Yahoo!Tankers site regarding the T34 Model 1942 glacis and driver hatch, resulting in the following:

1. glacis measured from 50mm to 55mm thickness

2. driver hatch was much thicker than glacis, measurement from photo suggests total hatch thickness is about 44% greater than glacis (70mm hatch thickness for 50mm glacis, 65mm thick hatch for 45mm glacis)

So, it appears that widely varying penetration ranges against T34 could be due to thickness variations.

75mm L43 hits on a 50mm thick T34 glacis would be resisted by 110mm vertical effective armor after high hardness decrease (0.79 multiplier), which would result in 7% penetration probability for 75L43 at 1250m. Add a few millimeters to the glacis armor, or a slight side angle, and T34 would be "safe" at 1235m as noted in George Forty's book.

When Germans reproduced T34 armor plates for May 1942 firing tests, they used a thickness range of 42mm to 53mm, which seems consistent with the measurements Jeff Duquette took.

[rexford]

went back and remeasured the T34 hatch areas several times after a good night's sleep.

top area of hatch that overlaps glacis is from 35% to 40% of glacis thickness.

[rexford]

Originally posted by Sardaukar:

Any idea if hit could break the whole hatch out of it's "hinges", so to speak ? That would render thickness relatively unimportant. Unlikely event, if correctly designed, but intriguing possibility.

Cheers,

M.S.

Read where 50mm guns were aimed at T34 driver hatch, which could have been to dislodge or break hinges, or to take advantage of edge effect penetrations.

[rexford]

Originally posted by Sardaukar:

Would that indicate that it's not a weak spot ? My first instinct says it doesn't depend so much about thickness, but arragement. But it indicates that Soviets were aware of possible weak spot.

Cheers,

M.S.

Russians could have been aware of great need to protect drivers.

[c3k]

Rexford,

Thank you for considering my hatch request with your usual thoroughness.

Sergei: your question about _inward_ hinged hatches is, of course, quite interesting. You obviously are confused with the rotating, middle-hinged hatch of the early war period. The Soviets knew that any hit on either the top or bottom of the middle-hinged hatch would cause it to rotate freely and quite rapidly. Because of this they placed the driver far enough back so the rotating hatch would not hit him. The Germans designed the MG-34 specifically to take advantage of this. The cyclic rate caused the hatch to spin so rapidly that it appeared invisible to the driver. This caused the driver to feel inadequately protected, and, after 5-7 seconds, the rapidly spinning hatch, continuously hit by a stream of 7.92mm bullets, caused extreme nausea and disorientation. Many sickened drivers veered away, ramming other T-34's, which would result in catastrophic, mushroom-cloud, explosive detonations. Hence, the redesigned hatch, which only opened _outwards_. Thank you for your suggestion.

Again, thanks for taking this up.

Ken

(Edited -again- because sarcasm causes me to forget how to spell. )

[ November 24, 2003, 08:46 AM: Message edited by: c3k ]

[Andreas]

Originally posted by c3k:

The Soviets knew that any hit on either the top or bottom of the middle-hinged hatch would cause it to rotate freely and quite rapidly. Because of this they placed the driver far enough back so the rotating hatch would not hit him. The Germans designed the MG-34 specifically to take advantage of this.

Hah! You are making it up. When the Germans designed the MG34, they had no idea about the T34.

I knew it, I knew it.

So what do you say now, Mr. Smartypants-r-down?

[Kanonier Reichmann]

Perhpas it was just a typo Andreas and he meant the MG42? Worth considering.

Regards

Jim R.

[Sergei]

Originally posted by Andreas:

Hah! You are making it up. When the Germans designed the MG34, they had no idea about the T34.

You idiot! If the Germans hadn't designed it as a counter-measure for T-34, then WHY would they have given it the name MG34? Note the exact same number... they could have called it as MG33, MG129, even MG34,01. But out of all possibilities they chose "34". That alone should tell us everything.

[MikeyD]

We've been burned once or twice before on that site. Remember the big stink about the 120mm bow on the late IS-2? And I had a long argument about the penetration ability of the 37mm gun on the BT-2 fast tank that was based on erronious reference material off that site.

Not to be hard on the site manager. Who among us hasn't quoted a line in good faith (usually form Chamberlain & Ellis) only to find out later it was inaccurate!?