Bow-crossing describes a harassment tactic in which a ship abruptly maneuvers to cross dangerously across the bow of another in violation of the 1972 International Regulations for Preventing Collisions at Sea (COLREG) and the 2014 Code for Unplanned Encounters at Sea (CUES). 

This maneuver is intended to force the other ship to take evasive action to avoid a collision. It may be used to disrupt freedom of navigation operations (FONOPS) or other assertions of international law or national sovereignty.

A recent example was documented in June 2023, when a Peoples Liberation Army Navy (PLAN) vessel crossed dangerously in front of U.S. Navy destroyer USS Chung-Hoon during a joint Taiwan Strait passage with the Canadian frigate HMCS Montreal, forcing the U.S. ship to reduce speed to avoid a collision:

China's ships use bow-crossing to protest the activities of other countries' ships in waters over which it claims sovereignty or jurisdiction, and to send the message that Beijing is willing to escalate tensions in defense of its claims.

In nautical terms, it involves a closest point of approach (CPA) of less than 2 lengths of the ship being intercepted. They are usually referred to by the U.S. Navy as "unsafe and unprofessional maneuvers".

Other examples: 

On September 30, 2018, the PLAN Type 052C Luyang II-class destroyer Lanzhou intercepted the U.S. Arleigh Burke-class destroyer USS Decatur, which was conducting a FONOP with 12 nautical miles of Chinese-occupied artificial islands in the South China Sea. The picture at the top of this post shows how close the two ships came to colliding.

On June 21, 2014, CCG vessel Haijian 2168 approached Vietnam Coast Guard (VCG) ship CSB 4032 at high speed. The VCG ship had to change directions repeatedly to avoid a collision as the distance between the two ships came within 30 meters. 

On December 5, 2013, a Chinese warship cut across the bow of the missile cruiser USS Cowpens at a distance of less than 200 yards in international waters.

In March 2009, five Chinese ships (a combination of PLAN, CCG and militia) harassed the U.S. surveillance ship USNS Impeccable in international waters in the South China Sea, forcing the American ship to make an emergency maneuver to avoid a collision.

See the rest of the playbook here.

Editor's note: This post was originally published on 7 July under the title "Unsafe Maneuvers", but was retracted when we decided to divide it into two separate categories. Apologies for any confusion.