Abstract
A realistic model of nucleon and pion interactions is developed incorporating fast development, possible formation of many pionisation centres and production of NN pairs. This model is use to develop air showers with proton primaries via the technique of successive generation. Comparison of the longitudinal properties of the resulting showers with experimental data at sea level suggests significant nucleon-anti-nucleon production (becoming more dominant for increasing energies) and the need for an even faster development.