In 1981 the United States Air Force bought eight American Airlines Boeing 707-320C aircraft at a cost of around 1.5 million dollars each with the initial intent to modify four of these aircraft to replace four of the aging EC-135N ARIA Aircraft.
81-0891 was the first of the American Airlines aircraft to be modified for the ARIA mission. The modification of this first Boeing 707-320C aircraft involved 300,000 man hours.
The ARIA equipment was removed from one of the original eight ARIA EC-135N aircraft and installed in 81-0891.
On January 4, 1985 ARIA aircraft 81-0891 was placed in the United States aircraft inventory as the only EC-18B in existence.
The equipment installed in 81-0891 was the typical ARIA setup with the addition of the SMILS system. SMILS was the Sonobouy Missile Impact Locating Systems which was used to score MIRV re-entries in the Kwajalein and Kodiak ranges.
The SMILS aircraft had the left wing painted black with red insignia. The blacken wing reduced glare reflected off the wing during re-entry. This reduced the glare to the high-speed cameras that filmed out of the port windows.
Source: Randy L. Losey