Which weapon system is primarily designed for anti-submarine operations?

The Mk 64 Mod 0 torpedo is specifically designed for anti-submarine operations. Torpedoes are weapons that are launched underwater and are intended to target submarines or other underwater vessels. The Mk 64 Mod 0 torpedo utilizes advanced guidance systems and has capabilities that make it well-suited for detecting and engaging submarines, which typically operate below the ocean's surface.

In contrast, cruise missiles, such as the Tomahawk, are designed for precision strikes against land or surface targets and are not optimized for underwater engagements. The Sidewinder missile is an air-to-air missile, predominantly used to combat enemy aircraft, and has no relevance to submarine warfare. Similarly, the Hellfire missile is primarily utilized for close air support against land targets, making it unsuitable for anti-submarine operations.

Thus, the Mk 64 Mod 0 torpedo's specific design and function for engaging submarines make it the correct choice for this question regarding weapons systems focused on anti-submarine operations.