The SU used both, a 20% and 80% criterium. They used for explorative performance trial and service acceptance proof G(D), a close to 100% ballitic criterium (5 out of 5 successes for the calibre in question at narrow valicty range, no failures allowed), which is the most severe penetration definition used by any nation during ww2. The CIOS report 'Steel AP and Theory of penetration' disprooves this myth. Germany never used a 50% criterium, and I don´t understant why this is going to be repeated here over and over again. It is, however, not comparable to defintions in place in Germany or the SU. This is comparable to US Navy ballistic limit. The criterium of penetration by definition in the 1950 british primary source was W/R complete penetration 50% probability criterium as used by the UK in late war contexts.
