Several successful underwater saboteur attacks during the Second World War proved the effectiveness of underwater sabotage. Terrorist attacks launched on the United States Navy’s destroyer USS Cole in October 2000 and French flag state tanker” Limburg” in 2002 illustrate the danger of terrorist attacks against the sea transport. The use of divers for Al-Qaeda attack on “Limburg” and several separatist underwater attacks on government vessels in Sri Lanka have proved the growing threat of this kind of terrorism against sea transport today. The active membership of the Republic of Latvia in NATO-led counter-terrorism and peace keeping operations as well as the growing role of the port of Riga in NATO Northern Distribution Network have made Latvia a potential target for terrorist attacks. This threat requires the necessity of increasing underwater security in the port of Riga.