The Lockheed EP-3 Aries II is the signals reconnaissance version of the P-3 Orion, operated by the United States Navy.
- EP-3A: Seven modified for electronic reconnaissance testing.
- EP-3B: Least known of all in the P-3 family. Three P-3As (BuNo 149669, BuNo 149673, and BuNo 149678) were obtained by the CIA from the US Navy under Project STSPIN in May 1963, as the replacement aircraft for CIA's own covert operation fleet of RB-69A/P2V-7Us. Converted by Aerosystems Division of LTV at Greenville, Texas, the three P-3As were simply known as "black" P-3As under Project Axial. Officially transferred from US Navy to CIA in June/July 1964. LTV Aerosystems converted the three aircraft to be both ELINT and COMINT platforms. The first of the three "black" P-3As arrived in Taiwan and were officially transferred to ROCAF's top secret "Black Bat" Squadron on June 22, 1966. Armed with 4 Sidewinder short range AAM missiles for self-defense, the three "black" P-3As flew peripheral missions along the China coast to collect SIGINT and air samples. When the project was terminated in January 1967, all three "black" P-3As were flown to NAS Alameda, California, for long term storage. Two of the three aircraft (BuNo 149669 and BuNo 149678) were converted into the only two EP-3Bs in existence by Lockheed at Burbank in September 1967, while the third aircraft (149673) was converted by Lockheed in 1969–1970 to serve as a development aircraft for various electronic programs. The two EP-3Bs, known as "Bat Rack", owing to their period of service with Taiwan's "Black Bat" Squadron, were issued to the US Navy's VQ-1 Squadron in 1969 and deployed to Da Nang, Vietnam. Later, the two EP-3Bs were converted to EP-3E ARIES, along with 10 EP-3As. The 12 EP-3Es retired in 1990s, when replaced by 12 EP-3E ARIES II.
- EP-3: ELINT aircraft for the Japanese Maritime Self-Defense Force.
- EP-3E Aries: 10 P-3As and two EP-3Bs were converted into ELINT aircraft
- EP-3E Aries II: 12 P-3Cs were converted into ELINT aircraft. Last delivered in 1997.
- EP-3J: Two, modified from P-3As, for FEWSG were uses as simulated adversary EW platforms in exercises; later transferred to the former Tactical Electronic Warfare Squadron 33 (VAQ-33), then transferred to the former Fleet Air Reconnaissance Squadron 11 (VQ-11).