Which of the following is a capability of the M2 .50 cal?

The M2 .50 caliber machine gun is renowned for its capability in anti-aircraft defense. It is designed to deliver a powerful, sustained rate of fire, which makes it effective against low-flying aircraft and targets at a relatively long distance. The .50 caliber round is highly destructive and is capable of penetrating armor, which adds to its effectiveness in aerial engagements.

While the M2 has been utilized in various roles such as ground support and vehicle mounted configurations, its primary advantage lies in its ability to provide a defensive strategy against aerial threats. Other options like underwater operation, close-quarters firefighting, and long-range sniping do not align with the intended design and operational capabilities of the M2. Each of these roles requires specific attributes that are outside the operational focus of the .50 cal machine gun.