two prototypes were built, the first flying in mid-1931. the second strengthened i-zbis flew at the beginning of the following year. these were followed by 21 examples ordered as evaluation aircraft and 50 production machines. by the time this last batch was being delivered, however, it was already apparent that the concept of a "single-shot" fighter was flawed and the i-zs that had been built were relegated to various testing roles. one such role was as a parasite fighter in the zveno project.