Glossary

Plain-language definitions of terms used across PGSA.IO incident reports and explainers. Each definition links to the primary-source authority for that term. This is a reference, not advice.

UKMTO — UK Maritime Trade Operations: The Royal Navy's 24-hour watchkeeping organisation for merchant vessels operating in the Indian Ocean region, Gulf of Oman, and Arabian Sea. UKMTO operates under UK Maritime Trade Operations and acts as the primary point of contact between the Royal Navy and commercial shipping in the region. Vessels are encouraged to register and report positions regularly while in the Voluntary Reporting Area. Official site: ukmto.org. See also: UKMTO explained.
NAVCENT — U.S. Naval Forces Central Command: The U.S. Navy component command responsible for the Middle East area of operations, including the Persian Gulf, Red Sea, Gulf of Aden, and Arabian Sea. NAVCENT is headquartered in Bahrain and commands Combined Maritime Forces. It publishes maritime advisories and press releases at navcent.navy.mil.
CMF — Combined Maritime Forces: A 47-nation naval coalition headquartered in Bahrain that conducts maritime security operations across approximately 3.2 million square miles of international waters. CMF comprises three combined task forces: CTF 150 (maritime security and counter-narcotics), CTF 151 (counter-piracy), and CTF 152 (Persian Gulf maritime security). Official site: combinedmaritimeforces.com.
CTF 152 — Combined Task Force 152: The CMF task force responsible for maritime security in the Persian Gulf. CTF 152 conducts maritime security operations, builds partner-nation capacity, and promotes security, stability, and prosperity across its area of operations. It is one of three CMF combined task forces. See CMF CTF 152 page.
CTF 153 — Combined Task Force 153: The CMF task force established in 2022, responsible for maritime security in the Red Sea, Bab-el-Mandeb Strait, and associated international waters. CTF 153 was stood up in direct response to escalating Houthi attacks and Iran-linked maritime threats in the region. See CMF CTF 153 page.
IMO TSS / TSS — Traffic Separation Scheme: A routing measure formally adopted by the International Maritime Organization that divides opposing streams of vessel traffic into separate inbound and outbound lanes, with a separation zone or line between them. The Strait of Hormuz has an IMO-approved TSS. Mariners are expected to comply with COLREGS Rule 10 when operating in a TSS. IMO publishes TSS charts and amendments at imo.org.
IRGC — Islamic Revolutionary Guard Corps: An Iranian armed force established after the 1979 revolution, constitutionally separate from Iran's conventional military. The IRGC controls significant economic assets within Iran and operates military, intelligence, and paramilitary functions. On 8 April 2019, the U.S. State Department designated the IRGC as a Foreign Terrorist Organization, the first time a state military force received this designation. State Department designation notice.
IRGCN — IRGC Navy: The naval arm of the Islamic Revolutionary Guard Corps. The IRGCN operates fast-attack craft, submarines, and maritime assets in the Persian Gulf and Strait of Hormuz. It is organizationally and operationally distinct from IRIN (the Islamic Republic of Iran Navy, which is Iran's conventional navy). Incidents attributed to the IRGCN in UKMTO and NAVCENT reporting are distinct from those attributed to IRIN.
IRIN — Islamic Republic of Iran Navy: The conventional naval force of the Islamic Republic of Iran. IRIN operates surface combatants and submarines and is separate from IRGCN (the IRGC Navy). The distinction between IRIN and IRGCN is relevant to sanctions analysis and incident attribution: the two forces have separate command structures. Iran's constitution gives the IRGC and the conventional military parallel authority in different domains.
FTO — Foreign Terrorist Organization: A designation made by the U.S. Secretary of State under Section 219 of the Immigration and Nationality Act (8 U.S.C. § 1189). Knowingly providing material support or resources to a designated FTO is a federal crime under 18 U.S.C. § 2339B. The current list of designated FTOs is published by the U.S. State Department at state.gov/foreign-terrorist-organizations. The IRGC is a designated FTO as of 8 April 2019.
OFAC — Office of Foreign Assets Control: A U.S. Department of the Treasury financial intelligence and enforcement agency that administers and enforces economic and trade sanctions based on U.S. foreign policy and national security goals. OFAC administers comprehensive Iran sanctions programs. OFAC's sanctions list search, recent actions, and FAQs are published at ofac.treasury.gov. See also: OFAC Iran-related transit actions digest.
P&I — Protection and Indemnity: A form of mutual marine insurance providing third-party liability cover for shipowners and operators. The principal P&I associations are members of the International Group of P&I Clubs, whose combined fleets represent over 90 percent of the world's oceangoing tonnage. P&I clubs provide guidance on war-risk routing and may impose additional conditions or exclusions for vessels transiting the Strait of Hormuz. The International Group of P&I Clubs is at igpandi.org.
IMO — International Maritime Organization: The United Nations specialized agency responsible for the safety and security of international shipping and the prevention of marine pollution. IMO adopts international conventions including SOLAS, MARPOL, and the ISPS Code. It maintains the GISIS database of ship and company information. Official site: imo.org.
IMB PRC — International Maritime Bureau Piracy Reporting Centre: The International Maritime Bureau's 24-hour duty centre for reporting and tracking piracy and armed robbery against ships worldwide. The IMB PRC is operated by the ICC's Commercial Crime Services division and publishes a quarterly piracy report. Contact and reporting information is at icc-ccs.org/imb.
MARSEC — Maritime Security level: A U.S. Coast Guard threat-level system for U.S. ports and vessels, running from MARSEC 1 (normal operations) through MARSEC 2 (heightened security measures) to MARSEC 3 (exceptional security measures in response to a credible threat). MARSEC levels are analogous to ship-security levels under the IMO's International Ship and Port Facility Security (ISPS) Code. Current MARSEC levels are published by the U.S. Coast Guard at dhs.gov/maritime-security-levels.
BMP5 — Best Management Practices, 5th edition: The fifth edition of Best Management Practices, a joint industry publication providing guidance for vessels transiting high-risk areas. BMP5 is produced by BIMCO and co-published by a consortium of shipping associations. It covers self-protection measures, reporting procedures, and working with naval forces. The document is freely available from bimco.org.
JWLA — Joint War Listed Areas: Areas designated as high-risk by the Lloyd's Market Association Joint War Committee (JWC), triggering an additional war-risk premium for hull insurance on vessels entering those areas. The Persian Gulf and Strait of Hormuz appear on the JWLA. The current listed areas are published by the Lloyd's Market Association at lmalloyds.com.
PGSA — Persian Gulf Strait Authority (disambiguation): The Persian Gulf Strait Authority is an Iranian state entity operating at pgsa.ir as the official interface to the IRGC for vessel transit arrangements in the Strait of Hormuz. PGSA.IO (this site) is an independent observatory with no affiliation to that entity. We are not the Persian Gulf Strait Authority. We do not collect fees, issue clearances, or represent any government. See pgsa.ir explained and About for the full independence statement.
VLCC — Very Large Crude Carrier: A tanker vessel class in the range of 200,000 to 320,000 deadweight tonnes, used primarily for long-haul crude-oil transport. VLCCs represent a significant share of the volume transiting the Strait of Hormuz, which is the only sea route for VLCCs exporting Gulf crude to global markets. IMO ship classification information is at imo.org/ship-types.
Project Freedom: A U.S.-led maritime initiative providing a transit umbrella and naval coordination framework for commercial vessels transiting the Strait of Hormuz. For a full explainer of the program, see Project Freedom on this site.