Which 4,000-pound penetrator bomb is used as the warhead/bomb body for the GBU-28A/B?

The BLU-113 is the correct answer because it is specifically designed as a 4,000-pound penetrator bomb used for deep penetration against hardened targets. This bomb utilizes a robust warhead and is constructed to penetrate reinforced structures, making it suitable for use in the GBU-28A/B, which is a laser-guided bomb designed for striking heavily fortified targets.

The GBU-28A/B combines this penetrator capability with guidance features, allowing for precision strikes while maintaining the bomb's effectiveness against its intended targets. Understanding the specific characteristics and intended applications of different bomb types is essential for effective munitions systems operations. Other bomb types, such as the BLU-122, BLU-126, and BLU-129, while valuable in their own right, serve different tactical roles and are not utilized in the GBU-28A/B configuration.