Did you know…
Why was the EF-111A unique?
Short answer
During the 1991 Gulf War it was the only unarmed crewed aircraft to fly so deep into Iraqi airspace, usually accompanying strike packages on deep-penetration missions. It carried no weapons: its speed and acceleration were its main means of self-defense, and its defining feature was the AN/ALQ-99E jamming system, derived from the Navy's ALQ-99 fitted to the Prowler.

An unarmed electronic warfare aircraft
The EF-111A Raven is a now-retired electronic warfare aircraft. It carried no weapons: its speed and acceleration were its main means of self-defense. It was crewed by two people, a pilot and an electronic warfare officer. In 1991, during the Gulf War, 18 EF-111As flew combat missions against Iraq, usually accompanying strike packages on deep-penetration missions, and the EF-111A was the only unarmed crewed aircraft to fly so far into Iraqi airspace.
The AN/ALQ-99E jamming system
The Raven's main feature was the AN/ALQ-99E jamming system, developed from the Navy's ALQ-99 fitted to the Prowler. Its engines were later replaced by the more powerful TF30-P-9 used in the F-111D. The cockpit was reorganized: all flight and navigation instruments were moved to the pilot's side.
Conversions, cost, and retirement
The program covered 42 conversions, including two prototypes. The total cost of those converted airframes was $1.5 billion. The last EF-111s were retired on 2 May 1998.
More questions

Aviation history
Which was the most-produced American fighter of the Second World War?
The Republic P-47 Thunderbolt, of which 15,636 or 15,683 units were built, depending on the source. It was also one of the heaviest fighters of the conflict… more…

Aviation history
Who flew the E-66 at 2,149 km/h?
Konstantin or Vladimir Kokkinaki, depending on the source. Konstantin is credited with the absolute record on a closed 100 km circuit, at 2,148.66 km/h, set… more…

Fly-by-Owen (CC BY SA), vía commons Aviation history
How many I-11Bs were built?
Between 208 and around 450, depending on the source: one of the AISA I-11 reference sheets gives 208 examples built, while All-Aero speaks of around 400 built… more…

Aviation history
How many HH-53s could be converted to Pave Low III?
Eight HH-53C aircraft received an improved systems package and were redesignated HH-53H Pave Low III. The other figure in circulation, nine MH-53H and 32… more…

SCDBob (CC BY SA), vía commons Aviation history
What did the A129 Mangusta's armor protect?
The fuselage: the A129's airframe is armored and, according to All-Aero, designed to protect against 12.7 mm rounds, with partial protection against 23 mm… more…

Fly-by-Owen (CC BY SA), vía commons Aviation history
What landing gear and canopy did the AISA I-11B have?
According to one account, AISA reduced the cockpit canopy and fitted tailwheel gear on the production I-11B. All-Aero claims the opposite: the I-11B was… more…