The F-105G was the designation given to Wild Weasel F-105Fs which were fitted with greatly improved avionics. The designation EF-105F was temporarily applied to these aircraft, but their designation was eventually changed to F-105G.
The F-105G was fitted with the AN/APR-35, AN/APR-36, AN/APR-37, and AN/ALR-31 Radar Homing and Warning (RHAW) systems. Installation of the AN/ALR-31 required that the wingtips be redesigned, in which a pair of antennas took the place of the navigational lights, which were moved to the leading edge of the wingtip. In addition, the Itek APR-36 radar homing and warning system of Wild Weasel F-105Fs was replaced by the Itek Radar Direction Finding and Homing system, and the Bendix APS-107 target acquisition set was installed. The F-105G also carried extra sensing antennae on the nose. Among these were four triangular-shaped antennae located on the nose just behind the main radome. Most F-105Gs were fitted with a combat camera mounted in a protrusion fitted underneath the nose just behind the radome.
The F-105G was also fitted with two long, cylindrical blisters for internally-mounted self-protection jammers that were faired into the sides of the lower fuselage. This freed up the outer underwing pylons that were usually used to carry noise jamming pods such as the Hughes ALQ-71 or General Electric ALQ-87 so that they could now carry additional ordnance such as more Shrikes. These blisters carried the Westinghouse AN/ALQ-105 electronic countermeasures jamming transmitters. A cooling scoop for the associated electronics was mounted on the fuselage belly just ahead of the weapons bay.
It is often said that the presence of the side blisters is what distinguished an F-105G from and F-105F. However, it is more correct to say that it is the presence of the AN/ALR-31 RHAW set that distinguished a F-105G from an F-105F. The presence of this new set could be demonstrated by the presence of wingtip sensors that displaced the aircraft's navigation lights, which were moved further forward on the wing leading edges. About 14 early F-105Gs were were fitted initially with the AN/ALR-31 system but without side blisters. In addition, some F-105Fs were modified with side blisters prior to being brought up to F-105G standards (e. g. being retrofitted with AN/APR-35 and APS-107) while others received ALQ-105 and AGM-78 capability simultaneously.
Fourteen of the F-105Gs were further modified to carry and launch the General Dynamics AGM-78A Standard ARM ModO anti-radar missile. The Standard was an anti-radiation missile designed to have a higher performance, longer range, and larger warhead that that of the Shrike, which was at that time giving indifferent results in the SouthEast Asian war. It was based on the Standard RIM-66A ship-based surface-to-air missile, and fitted with a seeker head from the AGM-45 Shrike. It flies on a dual-thrust motor and steers with tail controls and very low aspect ratio fixed wings. The missile was 180 inches long, had a wingspan of 43 inches, and had a diameter of 13.5 inches. Launch weight was about 1400 pounds, maximum speed was Mach 2.5, and range was up to 35 miles. The Mod0 was fitted with the T1 seeker used by the Shrike, but this was replaced by the Maxson broad-band seeker of the main(Mod1) production version, the AGM-78B. This seeker is designed to attack search, GCI, SAM and other radar systems and is intended to enable the launching aircraft to attack from any direction and to turn away and get outside the lethal radius of enemy SAMs. In addition, later variants of the Standard could continue unerringly toward its target even if the enemy radar was switched off, having had placed in its computer memory the precise coordinates of the target before launch. Between November 1968 and June 1969, another 16 F-105Gs were modified to launch the AGM-78B. The Standard was so large and heavy that a special heavy-duty underwing pylon had to be developed to carry the missile. The Standard was typically carried underneath the inboard underwing pylons or underneath the centerline pylon. Sometimes, both Standards and Shrikes were carried, with the smaller Shrike being carried on the outboard underwing pylons.
Because of the additional electronic equipment, the F-105G had a slightly smaller internal fuel capacity than the F-105F. Total internal fuel capacity was 1051 US gallons, as compared to 1160 US gallons for the F-105F.
The first F-105Gs went to the 357th TFS of the 355th TFW based at Tahkli RTAFB during the second half of 1967. The 12th Tactical Fighter squadron of the 18th Tactical Fighter Wing, which had been detached to Korat RTAFB from Okinawa, was also equipped with the F-105G. Also provided with the G was the 17th WWS and the 6010th WWS (Ex 1th TFS Detachment 1), both from the 388th TFW based at Korat RTAFB. Unlike the single-seat F-105Ds which had been withdrawn from Southeast Asia in 1970, the F-105Gs remained in Vietnam until the end of US involvement in that unhappy conflict.
Following the US withdrawal from Vietnam, two F-105G squadrons (the 561st and 562nd) served with TAC's 35th TFW at George AFB until they were replaced by F-4Gs in 1980. This marked the end of Thunderchief service with the USAF. The surviving F-105Gs were passed on to the 128th TFW of the Georgia Air National Guard, which operated them until 1983.