Thursday, 21 June 2018

American Armour Quality

"Report on the quality and robustness of American armour plate
  1. About 1500 tons of armour plate (excluding the plate arrived in recent months), 10, 15, and 35 mm thick, arrived from the USA to the USSR.
  2. The chemical composition of the armour is similar to that of domestic 8S steel, aside from the addition of 0.04-0.08% of copper (our armour has no copper).
  3. Factory #177 tested 8 samples of American armour. All samples, when hardened according to technical requirements for 8S steel, produce a fibrous, dry fracture. All samples show slating along nearly the whole cross-section. Individual samples show layering. Results of metallographic inspection show that the samples have a large amount of nonmetallic particles.
  4. The mechanical characteristics of the American armour are as follows:
    1. Module of rupture: 152-165
    2. Stretching: 3.2-4.8
    3. Compression: 30.9-40.8
    4. Impact strength: 3.6-6.9
      The same characteristics for domestic armour with the same chemical composition are as follows:
    5. Module of rupture: 162-163
    6. Stretching: 9.6-10.5
    7. Compression: 37.6-45.0
    8. Impact strength: 6.9-7.16
  5. Out of 8 35 mm thick samples of American plate tested at factory #177, four samples failed trials, as they had back-spall that was greater than 4 calibers of the impacting shell. The samples that passed demonstrated brittle damage when fired upon (back-spall), but within the technical requirements. According to technical requirements, back-spall greater than 4 calibers is not permitted.
  6. Based on the above, the GABTU BTU declined the request of Deputy People's Commissar of Tank Production comrade Popov to lower the requirements for American plate, since the use of this kind of armour in its hull would reduce its tactical-technical characteristics and increase the amount of cracks developed during welding.
  7. In addition, the NKTP representative in the USA reported that several batches of inadequate armour were sent to the USSR (one rejected batch, several batches that failed spalling requirements).
  1. The inadequate American armour that was sent to the USSR must be rejected.
  2. The rest of the batches must be re-sorted by chemical analysis and mechanical testing. Unsatisfactory batches must be rejected.
  3. Batches that are satisfactory can be put into production.
  4. Propose that the NKTP and People's Commissariat of Foreign Trade increase the requirements for armour sent from the United States and instruct the representative in American to select armour sent to the USSR more carefully.
  5. Batches that fail the technical requirements may be used as structural steel when building tanks and SPGs.
Engineer-Colonel Rogachev."


  1. What's the date of this document?

    The upshot is that the US was dumping defective armor plate into Lend-Lease. No big surprise, I suppose. Wonder if this was manufacturers sneaking things past Uncle Sam so that they weren't "wasting" money and resources, if the government knew but didn't care, or if the government knew but making Lend-Lease quantities was more important than quality.

    1. Whoops, my bad, I keep forgetting the dates. It's December 12th, 1942, so it's possible that the steel was received there were higher priority issues.

  2. Why one would even try to harden the good quality US RHA (typically 225-245BHN) to the very high hardness levels as of 8-S soviet domestic grade armor (440-460BHN) is understandable when one takes into account the requirement to break up inferior soviet domestic AP-quality. US soft RHA is optimized for lower hardness realms.
    Notice the criterium of backspall =4.0 times cal/diameter as borderline of acceptable soviet armor quality. Most other services had the limit at 2.0 cal/diameter for backspall, instead (acceptance limit).

    1. Because the point in the first place was to get armour that matched Soviet chemical composition for use in Soviet hardening processes to build Soviet tanks. As always, you do not read, only write.