What must be studied to ensure forces can accomplish their mission before culminating in operational art?

Operational Reach is the correct answer because it encompasses the range and duration that a military force can effectively operate in a given environment. Understanding operational reach is crucial for planning and executing military missions, as it determines how far forces can project their capabilities and sustain operations over time. This concept allows commanders to visualize and assess the limits of their operational capacity, ensuring that forces can meet their mission objectives without overextending themselves or risking failure due to ineffective resource management.

In contrast, while operational security, strategic defense, and logistical sustainability are all important elements in military planning, they do not directly relate to the reach and capacity of forces in the same way that operational reach does. Operational security focuses on protecting sensitive information, strategic defense is concerned with the overarching defense strategies against threats, and logistical sustainability deals with ensuring that resources are available to support operations. However, without a clear understanding of operational reach, the effectiveness of these elements may be diminished, as commanders would lack the necessary insight into how far and for how long they can maintain operational effectiveness in achieving their objectives.