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Prepared by: U.S. Indo-Pacific Command Office of the Staff Judge Advocate (J06) & U.S. Pacific Fleet Legal Office (N01J)

Last Updated: November 2, 2023 (all prior versions obsolete)

**This TACAID includes legal opinion and analysis that does not necessarily reflect official U.S. government positions.

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USINDOPACOM J06/SJA TACAID SERIES

TOPIC: International Regulations for the Prevention 

of Collisions at Sea (COLREGS)

BLUF

 This TACAID is intended as a reference tool for U.S. forces and allies and partners who are committed to 

upholding rules for safe navigation and opposing actions that undermine these rules. 

 The 1972 Convention on the International Regulations for Preventing Collisions at Sea (COLREGS) is the 

preeminent framework for navigational rules to prevent collisions and enhance overall safety at sea.

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 The COLREGS apply to all vessels, including warships, auxiliaries, and government-owned or operated vessels. 

 The COLREGS apply in waters beyond the territorial sea of any coastal state (including contiguous zones, exclusive 

economic zones, and high seas) and, except where a coastal state has established different rules, in territorial 

seas, archipelagic waters, and inland waters.2

 The COLREGS serve as a universal regulatory system for all mariners that governs safe navigation, including 

principles for interactions between vessels at sea. U.S. forces strictly adhere to the COLREGS.

 The navigational rules in the COLREGS help inform compliance with other legal obligations for safe navigation, 

such as the “due regard” standard established in the United Nations Convention on the Law of the Sea (UNCLOS). 

WHY THIS MATTERS

 The prevalence of some of the world’s most heavily trafficked sea lanes in the Indo-Pacific region underpins the 

need for all nations to uphold and comply with the COLREGS to ensure navigational safety. 

 The importance of the COLREGS is increasingly apparent as the People’s Republic of China (PRC) employs tactics 

to advance its excessive maritime claims by impeding the navigational rights and freedoms of other nations. 

 In the face of such tactics, adherence to the COLREGS is especially critical to avoid collision, mitigate risk of 

miscalculation/escalation, and prevent the erosion of international law and the rules-based international order. 

 The COLREGS comprise broadly accepted international rules – at least 155 nations have ratified the COLREGS, 

including the United States and the PRC, which represents approximately 99% of all global shipping.3

 The COLREGS apply to all vessels and do not include a military exemption – all warships, auxiliaries, and 

government-owned or operated vessels are obligated to comply with the COLREGS. 

 The COLREGS are an important part of the international legal framework governing operations at sea. With its 

focus on procedures for safe navigation, the COLREGS inform compliance with other legal obligations, such as 

those arising under UNCLOS and other international agreements.

 As professional mariners, Commanding Officers of warships of all nations have a legal obligation to diligently 

comply with the COLREGS by exercising the seamanship mandated by law and custom. 

 When vessels act contrary to the letter and spirit of the COLREGS, it creates potentially dangerous incidents at 

sea, causes friction between seafaring nations, and undermines the rules-based international order.

 U.S. Indo-Pacific Command stands with its allies and partners in reinforcing international law, rules, and norms 

that ensure safe maritime operations and help to maintain a free and open Indo-Pacific.
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DETAILED DISCUSSION

HISTORY AND APPLICABILITY OF THE COLREGS

 Adopted in 1972 and entering into force in 1977, the COLREGS 

updated and replaced the earlier Collision Regulations of 1960 

which were adopted at the same time as the 1960 Safety of Life at 

Sea (SOLAS) Convention. These prior regulations were also based 

on multiple separate conventions and practices dating back to the 

1800s that sought to codify centuries of maritime maneuvering 

and navigation customs.

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 Following ratification, the United States codified the COLREGS in 

U.S. Federal law in 1977.

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 A subsequent effort to similarly 

update the U.S. rules of navigation on inland waters resulted in 

the Inland Navigation Rules Act of 1980.6 With limited 

exceptions, the International and Inland Rules and Annexes are 

very similar in both content and format.

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 In keeping with the COLREGS’ universal applicability to vessels, 

including warships and naval auxiliaries, U.S. Navy Regulations 

direct that all persons responsible for the operation of naval 

ships and craft shall diligently observe the COLREGS.

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 The widely-accepted nature and applicability of the COLREGS 

have made it a binding aspect of customary international law that 

applies even to non-signatories.9 As such, the COLREGS are a

critical component of the international legal framework 

governing operations at sea. 

COLREGS AND OTHER INTERNATIONAL LAW AND AGREEMENTS

 Insofar as the COLREGS establish minimum required obligations for safe navigational practices, the COLREGS 

likewise inform compliance with other legal obligations governing navigation and interactions between vessels, 

such as those arising under UNCLOS and other bilateral/multilateral agreements. Key examples include: 

o UNCLOS: 

 Articles 58(1), 58(3), and 87(2) mandate that freedoms of navigation and overflight must be exercised 

with due regard for the rights and interests of all other nations. Compliance with the COLREGS helps 

inform adherence to this due regard standard.10 

o Bilateral Agreements: 

 U.S.–USSR Agreement on the Prevention of Incidents on and over the High Seas (INCSEA). This 1972 

agreement between the United States and USSR (later adopted by Russia) aimed to minimize 

harassing actions and promote safety. A principal element of INCSEA required both nations to strictly 

observe the letter and spirit of the COLREGS.11 

 U.S.–PRC Memorandum of Understanding (MOU) Regarding the Rules of Behavior for Safety of Air and 

Maritime Encounters (Rules of Behavior). This 2014 non-legally binding MOU is designed to 

strengthen adherence to and reinforce international law in encounters between ships from the two 

nations, particularly the safety of navigation principles enshrined in the COLREGS. Similar to the 

COLREGS, the Rules of Behavior encourages early and active communication during encounters to 

enhance safety and promote freedom of navigation.

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o Multilateral Agreements:

 Western Pacific Naval Symposium (WPNS) Code for Unplanned Encounters at Sea (CUES). After a 

decade of negotiation between Pacific nations, the 2014 Western Pacific Naval Symposium adopted 
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CUES as a non-binding agreement to reduce the chance of an incident at sea between the countries in 

the agreement, and — in the event that one occurs — to prevent it from escalating.13 Twenty one 

countries have joined the agreement, including Russia, the PRC, and the United States.14 Navies from 

all participating nations are expected to comply with the COLREGS as a foundational safety 

requirement during all encounters between vessels at sea.15 

COLREGS ORGANIZATION

 The COLREGS include 41 rules, divided into six 

sections, designed to prevent collisions at sea:

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o Part A: General Provisions

o Part B: Steering & Sailing

o Part C: Lights & Shapes

o Part D: Sounds & Lights

o Part E: Exemptions

o Part F: Verification & Compliance 

 Four annexes provide additional technical details 

concerning signaling (lights, shapes, sounds) and 

signals for fishing vessels when operating in close 

proximity, international distress signals, etc.

KEY COLREGS DEFINITIONS

 Vessel: “Vessel” includes every description of water craft, including non-displacement craft and seaplanes, used 

or capable of being used as a means of transportation on water.

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 Vessel Not Under Command: a vessel through some exceptional circumstance is unable to maneuver as required 

and is therefore unable to keep out of the way of another vessel.18

 Vessel Restricted in her Ability to Maneuver: a vessel, which from the nature of her work, is restricted in her 

ability to maneuver and is therefore unable to keep out of the way of another vessel. The term vessels restricted 

in their ability to maneuver shall include but not be limited to:

o Vessel engaged in laying, servicing, or picking up a navigational mark, submarine cable, or pipeline;

o Vessel engaged in dredging, surveying, or underwater operations;

o Vessel engaged in replenishment or transferring persons, provisions or cargo while underway;

o Vessel engaged in the launching or recovery of aircraft;

o Vessel engaged in mine clearance operations;

o Vessel engaged in severely restricting towing operations19

SUMMARY OF KEY COLREGS PROVISIONS20

 Rule 1 – Applicability: The COLREGS “apply to all vessels upon the high seas and in all waters connected therewith 

navigable by seagoing vessels.” 

 Rule 2 – Responsibility: Vessels are responsible for complying with the COLREGS and any precaution that may be 

required by the ordinary practice of seamen, to include due regard to all dangers of navigation and collision.

 Rule 5 – Lookout: “Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all 

available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the 

situation and of the risk of collision.”

 Rule 6 – Safe Speed: “Every vessel shall at all times proceed at a safe speed” as informed by several factors such 

as visibility, traffic density, environmental conditions, maneuverability, time of day, and the impact of radar.

 Rule 7 – Risk of Collision: “Every vessel shall use all available means appropriate to the prevailing circumstances 

and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist.”

A Chinese Coast Guard Vessel outfitted with a ramming device on the 

bow is depicted after bumping a Philippine supply vessel in the South 

China Sea on Oct. 22, 2023 (Armed Forces of the Philippines via AP). 
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 Rule 8 – Action to Avoid Collision: Any action taken to avoid collision shall be taken in accordance with Rules 4 

through 19 and must be with due regard to the observance of good seamanship.

 Rule 13 – Overtaking Situations: 

 Any vessel overtaking any other shall keep out of the way of the vessel being overtaken.

 A vessel shall be deemed to be overtaking when coming up on another vessel from a direction more than 

22.5 degrees abaft her beam, that is, in such a position with reference to the vessel she is overtaking, that 

at night she would be able to see only the stern light of that vessel but neither of her sidelights.

 When a vessel is in any doubt as to whether she is overtaking another, she shall assume that this is the 

case and act accordingly.

 Any subsequent alteration of the bearing between the two vessels shall not make the overtaking vessel a 

crossing vessel within the meaning of these Rules or relieve her of the duty of keeping clear of the 

overtaken vessel until she is finally past and clear.

 Rule 14 – Head-on Situations: Unless otherwise agreed, when two power-driven vessels are meeting on reciprocal 

or nearly reciprocal courses so as to involve risk of collision, each shall alter her course to starboard so that each 

shall pass on the port side of the other.

 Rule 15 – Crossing Situations: When two power-driven vessels are crossing so as to involve risk of collision, the 

vessel which has the other on her own starboard side shall keep out of the way and shall, if the circumstances of 

the case admit, avoid crossing ahead of the other vessel.

 Rule 16 – Action by Give-Way Vessel: “Every vessel which is directed to keep out of the way of another vessel 

shall, so far as possible, take early and substantial action to keep well clear.”

 Rule 17 – Action by Stand-On Vessel: “Where one of two vessels is to keep out of the way, the other shall keep 

her course and speed. The latter vessel may, however, take action to avoid collision by her maneuver alone, as 

soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate 

action in compliance with these Rules.” 

o When the vessel required to keep course and speed finds herself so close that collision cannot be avoided 

by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision

o This Rule does not relieve the give-way vessel of her obligation to keep out of the way.

 Rule 18 – Responsibilities Between Vessels: “A power-driven vessel underway shall keep out of the way of: (i) a 

vessel not under command; (ii) a vessel restricted in her ability to maneuver; (iii) a vessel engaged in fishing; (iv) a 

sailing vessel.

 Rule 20 – Lights & Shapes: 

o Rules concerning lights shall be complied 

with from sunset to sunrise (some 

exceptions apply)

o Lights prescribed by these Rules shall, if 

carried, also be exhibited from sunrise to 

sunset in restricted visibility and may be 

exhibited in all other circumstances when it 

is deemed necessary. 

o Rules concerning shapes shall be complied 

with by day.

 Rule 23 – Power-Driven Vessels Underway: A powerdriven vessel underway shall exhibit: (i) a masthead 

light forward; (ii) a second masthead light abaft of 

and higher than the forward one; except that a vessel 

of less than 50 meters in length shall not be obliged 

to exhibit such a light but may do so; (iii) sidelights; 

and (iv) a stern light.
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 Rule 27 – Vessels Not Under Command or Restricted in Their Ability to Maneuver:

o “A vessel not under command shall exhibit: (i) two all-round red lights in a vertical line where they can best 

be seen; (ii) two balls or similar shapes in a vertical line where they can best be seen; (iii) when making way 

through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.”

o A vessel restricted in her ability to maneuver, 

except a vessel engaged in mine clearance 

operations, shall exhibit: (i) three all-round 

lights in a vertical line where they can best be 

seen (the highest and lowest of these lights 

shall be red and the middle light shall be 

white); (ii) three shapes in a vertical line where 

they can best be seen (the highest and lowest 

of these shapes shall be balls and the middle 

one a diamond); (iii) when making way 

through the water, a masthead light(s), 

sidelights and a sternlight in addition to the 

lights prescribed in Rule 27(b)(i); (iv) when at 

anchor, in addition to the lights or shapes 

prescribed in Rule 27(b)(i) and (ii), the light, 

lights, or shapes prescribed in Rule 30.

 Rule 34 – Maneuvering & Warning Signals: 

o When vessels are in sight of one another, a power-driven vessel underway shall indicate that maneuver

by the use of signals on her whistle.

o When vessels in sight of one another are approaching each other and from any cause either vessel fails to 

understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken 

by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by use of her 

whistle and signal lights.

 Rule 36—Signals to Attract Attention: If necessary to attract attention, any vessel may make light or sound 

signals that cannot be mistaken for any signal authorized elsewhere in these Rules, or may direct the beam of her 

searchlight in the direction of the danger, in such a way as not to embarrass any vessel.

PROPOSED COUNTER-LAWFARE APPROACH

** This section offers suggested language for incorporation into communications strategies **

 The COLREGS establish navigational rules for ships to prevent collisions and enhance overall safety at sea. The 

COLREGS apply to all waters beyond the territorial sea of any nation and, except where a coastal state has 

established different rules, in territorial seas, archipelagic waters, and inland waters.

 Compliance with the COLREGS is legally binding on all vessels, including warships of all nations. This includes 

surface, subsurface, and unmanned systems—and all other government-owned vessels. 

 The COLREGS are an important part of the international legal framework governing safe navigation, including 

principles for interactions between vessels at sea.

 The rules contained in the COLREGS also inform compliance with other legal obligations, including bilateral and 

multilateral agreements such as UNCLOS. 

 All vessels are obligated to comply with the COLREGS in a professional manner that fosters safe navigation, 

protects life and property, and instills trust and confidence from the international community. Key requirements 

include communicating to nearby vessels in a timely and transparent manner, faithfully adhering to the letter and 

spirit of the rules, and executing maneuvers with the skill and seamanship required for safe navigation. 

 Adherence to the COLREGS is critical to avoid collision, mitigate risk of miscalculation, and prevent the erosion of 

international law and the rules-based international order. U.S. forces strictly observe to the COLREGS.
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1

See International Regulations for the Prevention of Collisions at Sea (COLREGS) (1972), available at 

https://www.imo.org/en/About/Conventions/Pages/COLREG.aspx.

2

See COLREGS, Rule 1; NWP 1-14M, The Commanders Handbook on the Law of Naval Operations (March 2022), para. 2.9.1. 

3

International Maritime Organization (IMO), Status of Conventions, available at 

https://imo.org/en/About/Conventions/Pages/StatusofConventions.aspx.

4

See IMO, Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs), available at 

https://www.imo.org/en/About/Conventions/Pages/COLREG.aspx; Wikipedia, International Regulations for Preventing Collisions at 

Sea, available at https://en.wikipedia.org/wiki/International_Regulations_for_Preventing_Collisions_at_Sea.

5 33 United States Code § 1601–1608

6 U.S. Coast Guard (USCG), Rules of the Road, available at https://www.dco.uscg.mil/NavRules/#:~:text=The%20United%20States

%20has%20ratified,Navigation%20Rules%20Act%20of%201977.

7

Id.

8 Article 1139, U.S. Navy Regulations (1990), available at https://www.secnav.navy.mil/doni/navyregs.aspx.

9

See e.g., Glen Plant, The Collision Avoidance Regulations as a Regulator of International Navigation Rights: Underlying Principles 

and their Adequacy for the Twenty-first Century, The Journal of Navigation, Volume 49 , Issue 3, pp. 377-393 (Sep 1996).

10 See United Nations Convention on the Law of the Sea (UNCLOS) (1982), available at 

https://www.un.org/depts/los/convention_agreements/convention_overview_convention.htm.

11 Agreement Between the Government of The United States of America and the Government of The Union of Soviet Socialist 

Republics on the Prevention of Incidents On and Over the High Seas (INCSEA) (1972), Article II, available at https://2009-

2017.state.gov/t/isn/4791.htm. NWP 1-14M, at 2.10.1. 

12 Memorandum of Understanding Between the Department of Defense of the United States of America and the Ministry of National 

Defense of the People’s Republic of China Regarding the Rules of Behavior for Safety of Air and Maritime Encounters (2014), 

available at https://dod.defense.gov/Portals/1/Documents/pubs/141112_MemorandumOfUnderstandingRegardingRules.pdf. The 

ROB specifically calls for military vessels to abide by the COLREGs. Id. at Annex II, Section I.

13 Western Pacific Naval Symposium, Code for Unplanned Encounters at Sea (CUES), Version 1.0, available at 

https://news.usni.org/2014/06/17/document-conduct-unplanned-encounters-sea. .

14 Id. 

15 CUES, para. 2.0.

16 See COLREGS.

17 COLREGS, Rule 3(a).

18 COLREGS, Rule 3(f). 

19 COLREGS, Rule 3(g).

20 This section does not comprise a comprehensive list of all COLREGS provisions, but rather a summary of key rules, including those 

most frequently violated.