 Besides USVs, the PCG is also rolling out the use of small police drones to assist in its checks on vessels difficult to board, such as loaded barges or vessels with low draft.The heightened global security alert following the 2001 September 11 terror attacks necessitated additional attention paid to preventing possible terrorist attacks by sea, a possibility underscored during the revelation of the Singapore embassies attack plot by the local Jemaah Islamiyah Islamic extremist group in December 2001, where it was revealed that Changi Naval Base was the subject of surveillance by them.There were also possible plans to bomb the United States Navy ships using the narrow channel between Pulau Tekong and Changi on the northeastern coast of Singapore.