One part of the U.S. National Drug Control Strategy is to disrupt the flow of cocaine through the transit zone. Puerto Rico and the U.S. Virgin Islands, the only U.S. territories located geographically within the transit zone, have served as entry points for cocaine destined for the continental United States. In recent years, federal and local government agencies have cited growing levels of violent crime in these territories and attribute this violence to illicit drug trafficking. Within DHS, the U.S. Coast Guard is the lead federal agency for maritime drug interdiction and a key provider of resources to support drug interdiction operations in the transit zone and the two territories. GAO was asked to examine the Coast Guard's drug interdiction efforts in the transit zone, Puerto Rico, and the U.S. Virgin Islands. This report addresses (1) trends in the Coast Guard's deployment of resources in the transit zone and the extent to which the Coast Guard met its performance targets; and (2) actions taken by the Coast Guard to combat drug smuggling into Puerto Rico and the U.S. Virgin Islands, and trends in vessel and aircraft deployments. GAO analyzed Coast Guard data for fiscal years 2009 through 2013 on drug interdiction resource deployments and mission performance, and interviewed Coast Guard and DHS officials involved in drug interdiction operations. GAO is not making recommendations in this report. DHS provided technical comments on a draft of this report, which were incorporated, as appropriate.