What system supports both tactical and strategic communications in the Navy?

The Global Information Grid (GIG) is the correct answer because it is designed to support both tactical and strategic communications within the Navy. The GIG encompasses a comprehensive network that facilitates the sharing of data among various military forces and supports joint operations, ensuring that commanders have access to the information they need for informed decision-making at all levels.

Unlike other systems, the GIG provides a unified architecture for communication, integrating various types of services and capabilities, including voice, data, and video. This multifaceted approach makes it essential for both day-to-day operations and larger operational strategies, aligning with the Navy's need for flexibility and adaptability in communication technologies.

The other options, while related to military communications, do not encompass the breadth and depth that the GIG does. For example, the Integrated Communications System is typically more focused on specific communication functions rather than the overarching network structure needed for both tactical and strategic communications. Similarly, the Global Defense Network and the Naval Operational Network serve important roles but do not fully capture the expansive scope and integrative capabilities provided by the Global Information Grid.