How does the GBU-53 small diameter bomb differ from the GBU-39?

The GBU-53 small diameter bomb (SDB II) is designed with advanced capabilities that allow it to effectively target moving targets, distinguishing it from the GBU-39 (SDB I). This is primarily due to its enhanced guidance system, which incorporates an advanced seeker that can operate in multiple modes such as millimeter-wave radar and electro-optical/infrared targeting. This multi-mode capability enables the GBU-53 to engage and track dynamic or moving targets with high precision, a feature not available in the GBU-39.

By contrast, other options highlight characteristics that do not align with the operational advantages of the GBU-53. Its accuracy is superior to that of earlier models, it does not feature a larger warhead, and while cost is a factor in manufacturing decisions, the GBU-53's advanced technology suggests that it may not necessarily be cheaper to produce. Overall, the GBU-53's ability to effectively target moving engagements is a key differentiator from its predecessor, the GBU-39.