What are the four levels of urban operations?

The four levels of urban operations are indeed best described as subterranean, street, building, and air. This classification is significant because it highlights the various operational environments encountered in urban settings, each requiring distinct strategies and tactics.

Subterranean operations involve navigating underground spaces such as tunnels, metro systems, or basements, which are often critical in urban combat to control movement and access. The street level includes open avenues and thoroughfares where direct engagements can occur. Building operations focus on close-quarters combat within structures, necessitating specialized tactics to secure rooms and manage civilian presence. Air operations refer to engagement from above, whether through surveillance, air support, or aerial delivery of supplies.

This framework is essential for understanding the complexities and diverse challenges that military and security forces face in urban warfare, as it requires adaptation to multiple environments within a single, densely populated area. In contrast, the other choices do not encapsulate the multifaceted nature of urban operations as effectively.