What phase of operations do adversaries primarily seek to defeat or deter US/coalition forces?

The correct choice highlights the critical phase of operations known as deployment, where adversaries aim to disrupt or deter US and coalition forces. This period is pivotal as troops and assets are being moved and positioned to engage in operations. Adversaries recognize that successful deployment is essential for operational effectiveness and can recognize that if they can hinder this phase, they can significantly affect the overall mission success.

During deployment, forces are often vulnerable while in transit and may be concentrated in specific locations, making them prime targets for adversary actions. By focusing their efforts on this phase, adversaries can exploit weaknesses and create challenges for the coalition forces before they even reach their operational roles.

The other phases, such as mission planning, operational sustainment, and post-deployment, while important, do not capture the same level of direct adversarial effort aimed at preemptively undermining the initial positioning and readiness of forces. These phases typically involve a more established presence and heightened security measures, thus reducing the effectiveness of disruption attempts compared to deployment.