Complex sentence: Four test flights of the High Virgo missile were conducted; due to development problems, the first two did not include the inertial guidance system, instead being fitted with a simple autopilot guiding the weapon on a pre-programmed course.
Split into simpler sentences: Four test flights of the High Virgo missile were conducted. Due to development problems, the first two did not include the inertial guidance system, instead they were fitted with a simple autopilot guiding the weapon on a pre-programmed course.