Operation Active Endeavour (OAE) was initiated in the immediate aftermath of the 9/11 terrorist attacks to deter, defend, disrupt and protect against terrorist activity. It helped to secure one of the busiest trade routes in the world and was among eight initiatives launched by the Alliance in 2001, in solidarity with the United States. It was an Article 5 operation, i.e., a collective defence operation that, initially, only involved NATO member countries until it started accepting non-NATO countries’ participation in 2004.

OAE hailed merchant vessels and boarded suspect ships, intervened to rescue civilians on stricken oil rigs and sinking ships and, generally, helped to improve perceptions of security. NATO ships also systematically carried out preparatory route surveys in "choke” points, as well as in important passages and harbours throughout the Mediterranean.

2010 was a turning point for OAE, when it shifted from a platform-based to a network-based operation, using a combination of on-call units and surge operations instead of deployed forces. In addition to tracking and controlling suspect vessels, it helped to build a picture of maritime activity in the Mediterranean by conducting routine information approaches to various vessels.

As part of the operation, NATO forces hailed over 100,000 merchant vessels and boarded some 155 suspect ships. Operation Active Endeavour was conducted first from Joint Force Command Naples, then NATO Maritime Command (MARCOM).