Homing Bomb System (HOBOS) | Specs
Research and Sources
The GBU-8/B and GBU-9/B were built around the Mk-84 2,000 lb (907 kg) general purpose bomb and the M118 3,000 lb (1360 kg) demolition bomb, respectively. Four cruciform tail fins with control surfaces allowed the weapon's flight path to be altered. Protruding ridges called strakes - in the same orientation as the fins - improved aerodynamic stability. An umbilical conduit running along the bomb connected the image-contrast guidance kit in the nose with the control fins in the back. In common with the Walleye this guided bomb needed a high-contrast aiming point on the target for a weapon 'lock'. With a sensor on the aircraft along with a control monitor in the cockpit for the Weapon System Officer the Homing Bomb System was ready for action.
In February 1969 the HOBOS is first used in combat. It also saw use on the first day of Linebacker 10 May 1972 in an attack on the Paul Doumer bridge. With a total length of over a mile (1.6 km) it was longer than the Thanh Hoa Bridge and arguably more critical of a choke point for the NVN rail system. But, the result was a disappointment as all the EOGBs launched missed. Another target only 20 miles (32 km) from the border with China the Lang Giai Railroad Bridge was 1,500 feet (460 m) long, supported by ten reinforced concrete piers up to 100 feet (30 m) high, with heavy concrete abutments at each end. This mission required authorization from the Joint Chiefs of Staff because of the proximity of the bridge to China. On 25 May 1972 twenty F-4 Phantom II's loaded with EOGBs and laser guided bombs in five flights of four attacked. The 1st flight released only two HOBOS by one aircraft because of the poor weather with up to 7/8th cloud cover. One weapon fell short and failed to detonate while the other was a direct hit, bringing down a span. The rest of the flights carried LGBs and engaged the bridge - after it was all over, six of 11 spans were down. Between 6 April and 30 June 1972, the 8th TFW destroyed 106 bridges with HOBOS and LGBs. Of the 500 EOGBs dropped in Southeast Asia between April and October 1972, 80% guided successfully and 52% scored direct hits. All together, more than 700 HOBOS were expended during the war.
|Name||GBU-8/B HOBOS||GBU-9/B HOBOS|
|Type||Electro-Optical Guided Bomb|
|In Combat||February 1969||?|
|# Used in Combat||more than 700||?|
|Warhead||2000 lb (907 kg) MK 84 bomb 1||3000 lb (1360 kg) M118E1 bomb 2, 3|
|Total Weight||2264 lb (1027 kg)||3420 lb (1551 kg)|
|Length||11 ft 11 in (3.63 m)||12 ft (3.66 m)|
|Diameter||18 in (46 cm)||25 in (63.5 cm)|
|Fin Span||3 ft 8 in (1.12 m)||4 ft 5 in (1.35 m)|
|Range||1,650 - 26,750 yards (1510 - 24460 m) 4||?|
|1||Mk-84 makes a 49-foot (15 m) wide, 13-foot (4 m) deep crater in medium soil with 946 lb (429 kg) explosive.|
|2||M118 with 1888 lb (856 kg) Tritonal explosive - a demolition bomb with a thin-casing and a greater blast effect but less cratering and penetration ability.|
|3||M118E1 is only different from the M118 in having threaded lug wells - similar to the M117 series of bombs.|
|4||Depending on launch altitude. Info from "A Compendium of Armaments and Military Hardware" by Christopher Chant|
Estimates vary by source, especially range and cost.
"Operation Linebacker I 1972 The first high-tech air war" by Marshall L. Michel III, Osprey publishing (ePub edition), 2019
"Rolling Thunder 1965-1968 Vietnam's most controversial air campaign" by Richard P. Hallion, Osprey publishing (ePub edition), 2018
"Linebacker The Untold Story of the Air Raids over North Vietnam" by Karl J. Eschmann, Lume Books (Kindle edition), 2018
"The Long Road to Desert Storm and Beyond" by Major Donald L. Blackwelder, School Of Advanced Airpower Studies, May 1992
"Second Generation Weaponry in SEA", HQ PACAF Directorate, Tactical Evaluation Project CHECO SEA Report, 10 September 1970
"Linebacker Operations September - December 1972", Project CHECO Office of History HQ PACAF 31 December 1978
Southeast Asia War Gallery of National Air Force Museum
Getting Closer: Precision Guided Weapons in the Southeast Asia War (National Air Force Museum)
National Archives Catalog
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