BLU-109 vs GBU-28

The United States military assigns hard-target defeat missions to two distinct munitions classes: the 5,000-pound GBU-28 and the 2,000-pound BLU-109. The GBU-28 is a complete, purpose-built weapon engineered for extreme depth, whereas the BLU-109 functions as a modular warhead integrated into standardized guidance kits. This architectural difference dictates their procurement scales, platform requirements, and target assignments.

Development and Design

The BLU-109 entered service in 1985. Lockheed Martin manufactured over 30,000 units, establishing it as the baseline 2,000-pound hard-target munition for Western air forces. It utilizes a 25.4mm forged steel casing and a mechanical-electrical delayed-action tail fuze. The GBU-28 originated as a rapid-prototyping effort during the 1991 Gulf War. The Watervliet Arsenal machined the initial bodies from deactivated 8-inch howitzer barrels in 14 days to engage Iraqi command centers buried below the BLU-109's reach. Subsequent GBU-28 variants replaced the artillery steel with specialized alloys housing the BLU-113 or BLU-122 warheads.

Performance and Capabilities

The payload-to-weight ratios reflect their differing engineering requirements. The BLU-109 is roughly 30% explosive by weight, while the GBU-28 allocates less than 15% of its mass to explosives, maximizing kinetic energy and casing integrity upon impact.

• The BLU-109 penetrates 1.2 to 1.8 meters of reinforced concrete. It carries 250 kg of Tritonal and integrates with standard tactical fighters, including the F-16 and F-35.
• The GBU-28 penetrates up to 6 meters of concrete or 30 meters of earth. It carries 286 kg of Tritonal or AFX-757. Its 5,824 mm length restricts it to the F-15E Strike Eagle and heavy bombers.

Guidance and Technology

The BLU-109 is an unguided steel body until mated with a tail kit. It integrates with Paveway II/III (GBU-10, GBU-24) and JDAM (GBU-31) systems, allowing target engagement via laser, GPS, or inertial navigation. The GBU-28 is a proprietary assembly originally reliant on Paveway III laser guidance. Later Enhanced GBU-28 (EGBU-28) variants incorporated GPS/INS to maintain accuracy in adverse weather. Both systems use delayed-action fuzing; however, 2011 USAF assessments identified premature detonation issues with GBU-28 fuzes during testing.

Deployment and Combat Record

The BLU-109 has seen combat employment across four decades. Configured as the GBU-31(V)3 JDAM, it was the baseline bunker-defeating weapon for coalition forces in Iraq, Afghanistan, and Syria. The GBU-28 is reserved for high-value, deeply buried targets. Two F-111Fs dropped the first units on the al-Taji airbase in 1991. F-15Es deployed them against the Straževica command center in Yugoslavia in 1999. Israel has utilized both systems extensively, dropping GBU-28s against subterranean Hamas infrastructure during the 2021 Guardian of the Walls operation.

Conclusion

The BLU-109 holds the edge in volume, versatility, and cost-efficiency. Paired with a JDAM kit, it equips multi-role fighter squadrons with a standard tool capable of defeating the majority of hardened shelters. The GBU-28 retains the edge strictly in sheer penetration depth. However, its reliance on specific heavy platforms and older architecture is driving the USAF to field the GBU-72 as its replacement, leaving the BLU-109 as the enduring standard for tactical hard-target defeat.