Six attacks against commercial vessels, the shoot-downs of a US Navy drone and an Iranian drone and the seizure of the UK-flagged 'Stena Impero' by Iranian authorities have caused disruption over the last months in the Strait of Hormuz, a major shipping route for world oil supply.

Reports by CNN this week say ships sailing in the region have reported unusual GPS interference, among other problems, and the US believes Iran is to blame.

With this respect, the US Department of Transportation's Maritime Administration issued a warning on Wednesday highlighting threats and advised vessels operating in this area to review security measures, ensure AIS is transmitting at all times, and monitor VHF Channel 16. Specifically:

1. To afford best protection in the region, US-flagged commercial vessels are encouraged to:

  • Simultaneously register with both the UK Maritime Trade Office (UKMTO) and US Fifth Fleet Naval Cooperation and Guidance for Shipping (NCAGS) Watch when entering the Indian Ocean Voluntary Reporting Area (VRA) by e-mailing them the Initial Report from Annex D of Best Management Practices to Deter Piracy and Enhance Maritime Safety in the Red Sea, Gulf of Aden, Indian Ocean and the Arabian Sea (BMP5).
  • Provide transit plans for the Strait of Hormuz (SoH) and Persian Gulf (PG) to UKMTO and US Fifth Fleet NCAGS via a single e-mail, including the time of entering/exiting the SoH Traffic Separation Scheme, an outline of the navigation plan for operating in the SoH and PG, and speed restrictions or other constraints.
  • In the event of any incident or suspicious activity, call UKMTO or the US Fifth Fleet Battle Watch and activate the Ship Security Alert System immediately.
  • Answer all VHF calls from coalition navies.
  • Utilize other reports included in Annex D of BMP5 as necessary, including both UKMTO and Fifth Fleet NCAGS on each of these reports.

2. All vessels should be aware that US and other coalition naval forces may conduct maritime awareness calls, queries, and approaches to ensure the safety of vessels transiting the Persian Gulf, Strait of Hormuz, Gulf of Oman, and Arabian Sea.

If a US flag commercial vessel suspects it is being hailed from a source falsely claiming to be a US or coalition naval vessel, the U.S. Fifth Fleet Battle Watch should be immediately informed.

3. If hailed by Iranian forces, US flag commercial vessels should provide vessel name, flag state, and affirm that they are proceeding in accordance with international law as reflected in the Law of the Sea Convention. The master should immediately inform the US Fifth Fleet Battle Watch.

4. If Iranian forces seek to board a US flag commercial vessel navigating these waters, the ship’s Master should, if the safety of the ship and crew would not be compromised, decline permission to board, noting that the vessel is proceeding in accordance with international law, and immediately inform the US Fifth Fleet Battle Watch.

5. If Iranian forces board a US flagged commercial vessel, the vessel should immediately contact the US Fifth Fleet Battle Watch. The crew should not forcibly resist the boarding party. Refraining from forcible resistance does not imply consent or agreement to that boarding.

6. The Maritime Global Security website at industry issued best practices, including BMP5, and guidance to mariners by geographic region and provides contact and subscription information for regional maritime security reporting centers.

7. Vessels operating in this area are advised to establish contact with both UKMTO and the US Fifth Fleet NCAGS Watch, and to include both on all update or incident report emails, as detailed above. By including both as addressees on each email, awareness will be enhanced without creating an additional reporting burden.