A marine threat monitoring and defense system and method protects a target vessel in icy or other marine regions. The system uses communications, user interfaces, and data sources to identify marine obstacles (e.g., icebergs, ice floes, pack ice, etc.) near a target vessel performing set operations (e.g., a stationed structure performing drilling or production operations or a seismic survey vessel performing exploration operations with a planned route). The system monitors positions of these identified marine obstacles over time relative to the target vessel and predicts any potential threats. When a threat is predicted, the system plans deployment of support vessels, beacons, and the like to respond to the threat. For example, the system can direct a support vessel to divert the path or break up ice threatening the target vessel.