increase survivability. Launcher and support equipment The M790 erector launcher (EL) was a modified low-boy flat-bed trailer towed by a Ford M757 5-ton tractor. The erection booms used a 3,000 psi pneumatic over hydraulic system that could erect the five ton missile from horizontal to vertical in nine seconds. Due to the overall missile length and for security, the warhead was not mated during travel. It was stored in a carrier and mated using a hand-pumped davit after the launcher was emplaced. The EL was pulled by a Ford M757 tractor for U.S. Army units and by a Magirus-Deutz Jupiter 6×6 for German Air Force units. The PTS and PS were mounted on a Ford M656 truck for U.S. Army units and a Magirus-Deutz or MAN SE for German Air Force units. Launch activation was performed from a remote fire box that could be deployed locally or mounted in the battery control central (BCC). One PTS controlled three launchers— when one launch count was complete, ten large cables were unplugged from the PTS and the PTS was moved up and connected to the next launcher. Further improvements Missile and power station upgrades in 1974 provided easier access to missile components, reduce maintenance and improved reliability. A new digital guidance and control computer combined the functions of the analog control computer and the analog guidance computer into one package. The mean time to repair decreased from 8.7 hours to 3.8 hours and the mean time between failures increased from 32 hours to 65 hours. More modifications in 1976 greatly reduced the launch time. The sequential launch adapter (SLA) was an automatic switching device mounted in a 10-ton trailer that allowed the PTS to remain connected to all three launchers allowing all three missiles to stay hot. The automatic reference system (ARS) eliminated the theodolites previously used to lay and orient the missile. It included a north-seeking gyro and a laser link to the ST-120 that more quickly oriented the missile. After the Pershing II explosion in 1985, the Pershing 1a launchers of the German Air Force were retrofitted with ballistic shields. In 1987 a joint Army/Department of Energy study concluded that it was technically and financially feasible to replace the W50 warhead carried by Pershing 1a with the W85 warhead developed for Pershing II. However, with the signing of the INF Treaty, development on the conversion was terminated. Gallery Pershing II