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 designed to fly at low altitude and attack targets deep inside enemy territory.
It carried the AN/AVQ-26 PAVE Tack infrared targeting designator/reader in a pod-mounted turret beneath the fuselage. This system allowed the aircraft to track and designate ground targets for laser, infrared, and electro-optical bombs. The F-111F was one of the most effective Allied aircraft in Operation Desert Storm in 1991, flying more than 2,400 sorties against Iraqi strategic sites, vehicle formations, and hardened bunkers.
After the ground war began on Feb. 24, 1991, efforts to destroy Saddam Hussein’s underground command-and-control network continued, culminating in the rapid development of a new weapon under Operation Deep Throat, which was intended to reach the deepest levels of his concrete bunkers.
As Peter E. Davies explains in F-111 & EF-111 Units in Combat, the Raytheon/Texas Instruments GBU-28 “Bunker Buster” was initially cleared for carriage only by the F-111F. The USAF would have preferred the weapon to be compatible with the F-15E, but technical limitations prevented that until after the war.
The bomb was improvised in a record two-month program to meet a specific need: destroying bunkers buried too deep for the standard BLU-109 penetrating warhead on the GBU-24. It was believed that about 40 bunkers in Baghdad sat as much as 50 feet below the surface, protected by two-foot-thick concrete slabs over networks of connected concrete tubes and chambers, each housing command-and-control facilities for more than 1,000 military personnel. The bunkers also held enough supplies for their occupants to remain underground for several weeks at a time.
Potential manufacturers of the weapon were given ten weeks to find a solution before Jan. 15, 1991, the date on which hostilities were expected to begin. A ready-made answer for the weapon’s body came when a Lockheed employee suggested using surplus, worn-out M201 howitzer barrels stored by the US Army. Two were shortened, rebored to a 10-inch internal diameter, fitted with 4,400-lb BLU-113 noses, and filled with 630 lbs of Tritonal explosive. Texas Instruments then attached the GBU-24’s WGU-36 guidance section and BSG-92 Airfoil Group — with clipped GBU-24-style canards and a tail and nose adaptor similar to the GBU-10’s MXU-651 — to the 13-foot body, and developed control parameters through computer simulation.
In the first test at Tonopah Range on Feb. 24, 1991, 431st TES F-111F 74-0186 — also used to test the PAVE Tack system — carried out the only GBU-28/B trial over desert terrain, where it penetrated to an inaccessible depth of more than 100 feet. Four days later, the bomb was used operationally in Iraq. A later test using a rocket-powered sled launched a GBU-28A/B at an array of steel-reinforced slabs about 22 feet thick. The bomb passed through the entire stack and kept going downrange for another 2,500 yards.
Two GBU-28/Bs were flown to Taif on a C-141 transport on Feb. 27, accompanied by a weapons systems officer from the 431st TES. His job was to brief the crews of the 48th TFW(P) selected for the first mission with the new weapon. Just 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. Armorers also added a single Mk 84 to offset the GBU-28/Bs’ 5,000-pound weight. Both aircraft were assigned to strike command bunkers beneath Al Taji air base, northwest of Baghdad, which had so far withstood F-117A attacks using GBU-27s. The two F-111Fs, “Cardinal 7-1” and “7-2,” could laser-mark the target for each other or designate 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 planned secondary target to the primary one. Analysis of the PAVE Tack VCR film showed the second weapon hitting the aim point, and moments later smoke was seen pouring from the bunker’s air vents. This suggested a devastating explosion inside the bunker. An Iraqi ceasefire the next day may have been prompted by this unexpected loss of their supposedly safe refuge, although Saddam was not in the Al Taji bunker. Other similar bunkers under Baghdad—the last refuge of Saddam’s high command—would also have been targeted if the conflict had continued.
The F-111E/Fs had flown their final Desert Storm mission. The GBU-28 was officially added to the USAF arsenal, and a later version, designated the GBU-37 and 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 by U.S. Air Force and DStorm.eu
