Complex sentence: To reduce this vulnerability, the Navy initiated the New Threat Upgrade (NTU) program, which consisted of a number of sensor, weapons and communications upgrades, intended to extend the service life of the ships.
Split into simpler sentences: To reduce this vulnerability, the Navy began the New Threat Upgrade (NTU) program. This consisted of a number of sensor, weapons and communications upgrades that were intended to extend the service lives of the ships.