Early demonstrations of the use of models in the U.S. and U.K. to assist in the determination of NDE reliability and probability of detection (POD), as dictated by the advent of damage tolerant design, will be reviewed. A major motivation in the U.S. was the adoption of POD as the primary metric for effectiveness of an inspection and the empirical observation that field and depot inspections were not adequate so support the desired structural integrity. In parallel, a series of round robin trials in Europe raised issues with the effectiveness of nuclear power plant inspections, and the resulting concerns became an important part of the “Public Inquiry” in the UK regarding the construction of the Sizewell B power plant. In each country, physics‐based models of the inspection process became an important part of the response. This paper describes these early developments in the use of models to assess inspection reliability, contrasts the philosophies and approaches taken, and notes how these provide the origins of NDE simulation activities today.