Tuesday, 5 February 2019

A Different Angle

There is a strangely prevalent opinion in some circles that everything there was to know about WWII was already known, and that any new information is completely unnecessary revisionism. Those people are naturally wrong, as illustrated pretty conclusively by Yuri Pasholok. Something as fundamental as a measurement went uncorrected for decades.

For instance, if you look up the values of front armour for the SU-122, you'll probably see 45 mm at 50 degrees for the upper front plate, 45 mm at 45 degrees for the lower front plate. This value seems universally accepted, but also wrong.

Both angles are off: the top plate is angled at 52 degrees from vertical, and the bottom is 60 degrees from vertical. This is not just a one-off measurement, and its pretty noticeable in other blueprints as well. A line sloped at 50 degrees is way off on the overall blueprints.

The SU-85 shows the same armour:

The pattern keeps going with the SU-100. SU-100 armour diagrams are closer to the truth, with an angle of 55 degrees on the bottom, as opposed to 60.

This discrepancy is shown not only on paper, but in metal. A measurement of the angle that the upper front plate meets with the roof is pretty clearly 52 degrees on both the SU-100 and SU-85.


  1. At last! This has been driving me nuts ever since the Tamiya Su-122 came out. Now there will be room to put the idler mount where it should be. Thank You!

  2. You can reason that measuring the glacis angle can be 2° off as the vehicle may not be sitting on level ground and those long guns may make the vehicle droop to the front. Bird and Livingston's book Armor and Gunnery has the lower front 45 @ 60°. In the diagram on the SU-100 it looks like he glacis and lower hull armor is the same thickness. Someone I know measured the glacis of one and it measures 75mm. But not the lower hull.

    1. The angle between the roof and front plate isn't going to change if the vehicle tilts forwards.

    2. Maybe they didnt account for the tilt and so their 0 degrees axis was off and the angles then became wrong.

    3. They are measuring the angle between the roof and the upper front plate, not the upper front plate and some arbitrary horizontal line. If the upper front plate is tilted, the roof will be tilted by the exact same angle, since the hull of the vehicle is rigid.

  3. If the effective slope is only 50° and on-coming shell doesn't care that the deck is at 2°. But, this would mean the lower hull is at an effective 62°.

    I'm concerned that the lower image shows the lower hull of the SU-100 with a 75mm thickness. Is this a post war modification?

  4. How are you getting 75mm? Are you measuring? I don't see it on the blueprint.

  5. There are blue-prints on the web or it is here:
    But then you can count pixels and compare the thickness to the 122 mm distance measurement on the plan.