MIM-104B (PAC-1)

The MIM-104B or standoff jammer countermeasures (SOJC) Patriot Advanced Capability (PAC-1), known today as the PAC-1 upgrade, was a software-only upgrade. The most significant aspects of this upgrade were changing the way the radar searched and the way the system defended its assets. Instead of searching low to the horizon, the top of the radar's search angle was lifted to near vertical (89 degrees) from the previous angle of 25 degrees. This was done as a counter to the steep parabolic trajectory of inbound ballistic missiles. The search beams of the radar were tightened, and while in "TBM search mode" the "flash", or the speed at which these beams were shot out, was increased significantly.

The MIM-104B adds a surface-to-surface capability against ground-based radar jamming sources to the Patriot system. The missile can fly an optimized (lofted) trajectory towards the jammer, and use its seeker to select the strongest emitter for terminal homing. The anti-aircraft/anti-missile capability is the same as for the MIM-104A.

It is designed to seek out and destroy ECM emitters at standoff ranges. It works similar to an anti-radiation missile in that it flies a highly lofted trajectory and then locates, homes in on, and destroys the most significant emitter in an area designated by the operator.

After a successful interception of a Lance missile in September 1986, PAC-1 was deployed in July 1988.