Analysis of the PAVE Tack VCR film showed the GBU-28 impacting at its aim-point, and moments later smoke was seen surging from the bunker’s air-vents. This indicated a devastating explosion within the bunker.
The F-111F was a long-range, all-weather strike aircraft capable of navigating at low level to destroy targets deep in enemy territory.
The aircraft was equipped with an all-weather AN/AVQ-26 PAVE Tack infra-red targeting designator/reader carried in a pod-mounted turret under the fuselage. It could track and designate ground targets for targets for laser, infra-red and electro-optical bombs. The F-111F was one of the most effective Allied aircraft in Operation Desert Storm (1991), flying more than 2,400 sorties against Iraqi strategic sites, vehicle formations and hardened bunkers.
After the ‘land war’ began on Feb. 24, 1991 attempts to destroy Saddam Hussein‘s underground command and control network continued, culminating in the rapid development of a new weapon as part of Operation Deep Throat that it was hoped would reach the deepest levels of his concrete warrens.
As explained by Peter E. Davies in his book F-111 & EF-111 Units in Combat, the Raytheon/Texas Instruments GBU-28 ‘Bunker Buster’ was initially only cleared to be carried by the F-111F. The USAF would have preferred that the weapon was compatible with the F-15E, but there were technical limitations that prevented this from happening until after the war.
The bomb had been improvised in a record two-month programme to meet a specific need — the destruction of bunkers that lay too deep for the standard BLU-109 penetrating warhead fitted to the GBU-24. It was thought that around 40 bunkers in Baghdad were buried up to 50 ft below the surface, with two feet-thick concrete slabs covering networks of interconnected concrete tubes and chambers, each of which housed command and control facilities for more than 1000 military personnel. The bunkers also contained sufficient supplies for their occupants to remain underground for several weeks at a time.
Potential manufacturers of the weapon were given a ten-week deadline to find a solution before Jan. 15, 1991 — the date on which it was assumed that hostilities would begin. A ready-made solution to the creation of a suitable body for the weapon came when a Lockheed employee suggested using surplus, worn-out M201 howitzer barrels stored by the US Army. Two examples were shortened, re-bored to ten inches internal diameter, fitted with 4400-lb BLU-113 noses and loaded with 630 lbs of Tritonal explosive. Texas Instruments mated the GBU-24’s WGU-36 guidance section and BSG-92 Airfoil Group (with clipped GBU-24-like canards and a tail and nose adaptor similar to the GBU-10’s MXU-651) to the 13-ft long body and devised control parameters using computer simulation.
In the first test at Tonopah Range on Feb. 24, 1991, 431st TES F-111F 74-0186 (also used to trial the PAVE Tack system) performed the only GBU-28/B test over the desert terrain, and it penetrated to an inaccessible depth of more than 100 ft. Four days later the bomb was used operationally in Iraq. A later test using a rocket-powered sled on rails launched a GBU-28A/B against an array of steel-reinforced slabs some 22 ft thick. The bomb passed through the whole stack and continued down-range for another 2500 yards!
Two GBU-28/Bs were flown to Taif by C-141 transport on Feb. 27, the weapons being accompanied by a WSO from the 431st TES. It was his job to brief the 48th TFW(P) crews that had been selected for the first mission with the new weapon. Only five hours after the bombs arrived, two F-111Fs (70-2391 — the 495th TFS commander’s aircraft — and 70-2387 from the 493rd TFS) were loaded. Armourers also uploaded a single Mk 84 to counterbalance the GBU-28/Bs’ 5000-lb weight. Both jets were tasked with targeting command bunkers beneath Al Taji air base, northwest of Baghdad, these having so far resisted F-117A bombing with GBU-27s. The two F-111Fs, ‘Cardinal 7-1’ and ‘7-2’, could laser-mark the target for each other or target-mark and guide their own weapons.
Lt Col Ken Combs and Maj Jerry Hust in the first F-111F narrowly missed the target, so they quickly diverted ‘Cardinal 7-2’ (70-2387), flown by Col David White and Capt Tommy Himes, from its intended secondary target to the primary. Analysis of the PAVE Tack VCR film showed the second weapon impacting at its aim-point, and moments later smoke was seen surging from the bunker’s air-vents. This indicated a devastating explosion within the bunker. An Iraqi ceasefire the following day may have been prompted by this unexpected denial of their supposedly safe retreat, although Saddam was not in the AI Taji bunker. Other similar bunkers under Baghdad — the last resort of Saddam’s high command — would also have been targeted if the conflict had continued.
The F-111E/Fs had flown their final mission of Desert Storm. The GBU-28 duly joined the USAF’s arsenal, and a developed version (designated the GBU-37), fitted with GPS, was made available for the B-2A Spirit.
F-111 & EF-111 Units in Combat is published by Osprey Publishing and is available to order here.
Photo credit: U.S. Air Force and DStorm.eu
