On 19 January 2016 the United States Coast Guard issued an alert (Safety Alert 01-16) reminding users that this past summer (2015), multiple outbound vessels from a non-US port suddenly lost GPS signal reception.

The net effect was various alarms and a loss of GPS input to the ship’s surface search radar, gyro units and Electronic Chart Display & Information System (ECDIS), resulting in no GPS data for position fixing, radar over ground speed inputs, gyro speed input and loss of collision avoidance capabilities on the radar display.

More on the subject with advice to mariners as to what they should do in
reporting disruption is to be found here.