Final answer:
The GBU-39 bomb is a precision-guided munition with an advanced penetrator warhead and a high strength steel case used by the US military.
Step-by-step explanation:
The student is asking which GBU-39 (Guided Bomb Unit-39) small diameter bomb is designed with an advanced penetrator warhead enclosed in a high strength steel case.
The GBU-39 bomb is a precision-guided glide bomb used by the United States military. It is designed to be more accurate than traditional unguided bombs, with a GPS-aided inertial navigation system to guide it to its target. The advanced penetrator warhead is designed to penetrate hardened structures before detonating, which is why it uses a high strength steel case. The subject matter of this question relates to advanced military engineering and weapons design. It is a highly specialized area of study, typically discussed at the college level or in a military academic context.