Which secure messaging system is used in tactical communications?

The Secure Internet Protocol Router Network (SIPRNet) is the correct choice for use in tactical communications because it is specifically designed to support secure, classified communications for military and government personnel. SIPRNet provides a secure means of transmitting data, including voice and video communications, which is crucial in tactical environments where data integrity and confidentiality are paramount.

SIPRNet operates on secure protocols that help to ensure that sensitive information is protected from unauthorized access, making it an essential tool for military operations. It supports secure messaging, allowing for real-time communications that are necessary for decision-making and coordination in challenging environments.

In contrast, other options like GPS, which is primarily for navigation and positioning, and commercial satellite communications, which may not provide the security required for classified information, do not fulfill the same role as SIPRNet in tactical communications. Additionally, open internet protocols do not offer the necessary security measures that military operations demand, making them unsuitable for handling classified messages.