Abstract This is the first of two papers that describe a new technique to measure yarn strains in a fabric subjected to ballistic impact. The main objective of this research was to develop the Nickel–Chromium (NiCr) wire technique, although other diagnostic techniques were used simultaneously (X-rays, high-speed video, and ultra-high-speed photography), to support interpretation of results. The NiCr wire principle, calibration, assumptions and test set-up are thoroughly explained. The NiCr wire is then applied to impact on real targets and the results are analyzed. A few examples of strain measurements are shown. It is shown that the NiCr wire signals are very rich in information and can give, not only the strains, but also reveal if the fabric was perforated and how long it took to fail.