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. In response to these threats, the PCG stepped up routine checks on vessels in Singapore's territorial waters, in particular on passenger ferries returning from regional destinations. Since late-2004, PCG officers have given additional training in the areas of boarding vessels for this purpose and are equipped with skills in the detection of explosives, drugs and fraudulent documents, courtesy of the Immigration and Checkpoints Authority's (ICA) provision of much assistance and training towards PCG in such an endeavour.