Operation Active Endeavour (2001-2016) was the first of its kind NATO Article 5 operation, enshrining the principle of collective defence. It was invoked for the first time after the terrorist attacks against the United States of 11 September 2001. It aimed to demonstrate NATO's solidarity and monitored shipping in the Mediterranean to help deter, defend, disrupt and protect against terrorist activity. NATO forces hailed over 100,000 merchant vessels and boarded some 155 suspect ships. By conducting these maritime operations against terrorist activity, NATO’s presence in these waters benefited all shipping travelling through the Straits by improving perceptions of security. The operation was succeeded in 2016 by maritime security operation Sea Guardian. The Sea Guardian currently performs three Maritime Security Operations tasks in the Mediterranean: support to Maritime Situational Awareness, support maritime Counter-Terrorism and contribute to maritime security capacity building.