 The Titan II used the LR-87-5 engine, a modified version of the LR-87, that used a hypergolic propellant combination of nitrogen tetroxide for its oxidizer and Aerozine 50 (a 50/50 mix of hydrazine and UDMH) instead of the liquid oxygen and RP-1 propellant of the Titan I.The first Titan II guidance system was built by AC Spark Plug.It used an Inertial measurement unit made by AC Spark Plug derived from original designs from the Charles Stark Draper Laboratory at MIT.