The warning system and message format

CANCEL THIS MSG

The warning's own expiry: a line telling the reader when the message cancels itself.

A warning about an operation with a known end — a rocket launch window, a firing exercise, a survey leg — usually ends with "CANCEL THIS MSG" and a date-time group. After that moment the warning is no longer in force, without any further broadcast.

seahazards records that time as the warning's self-cancellation. An expired warning stops being current, but its expiry does not show that the operation finished on time or that the area is clear; a coordinator can also issue a new warning that extends or replaces it.

What the archive shows

95,350 messages in this archive use “CANCEL THIS MSG”, the earliest issued 1993-06-03 and the latest 2026-09-24. 72 of them are in force in the latest lists we collected. A hazard reported again and again counts once per message.

The largest yearly count is 2019, with 5,602 messages. Collection is incomplete between 2024-05 and 2026-08-17, so 2024, 2025 and 2026 are not comparable with fully collected years.

Exercises accounts for 35,342 of 95,350 recorded messages (37%), the largest warning type group in this selection.

Located messages that use it fall in 94 sea areas; the most frequent are South Atlantic Ocean (13,573), North Atlantic Ocean (8,376) and North Pacific Ocean (7,133).

Its use is spread fairly evenly through the year: the busiest month, March, has 8,667 messages and the quietest, July, 7,320.

By warning series: HYDROLANT 39,433, HYDROPAC 35,385, NAVAREA IV 12,522 and NAVAREA XII 5,555, and 6 more.

Messages using it, by year of issue

'93
'94
'95
'96
'97
'98
'99
'00
'01
'02
'03
'04
'05
'06
'07
'08
'09
'10
'11
'12
'13
'14
'15
'16
'17
'18
'19
'20
'21
'22
'23
'24
'25
'26

By month of issue, all years

Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Where it appears · 94 sea areas

In force now · 72

  1. NAVAREA XI 426/26 · Cable ops · South China Sea2026-09-24 · in force

    …UNTIL 08 OCT 2026. IN VICINITY OF A.11-38.23N 118-56.36E. B.11-34.10N 118-53.54E. CANCEL THIS MSG 091600Z OCT.

    Submarine pipeline works by M/V fortitude →
  2. NAVAREA XI 425/26 · Missiles2026-09-23 · in force

    …180-00W 29-41N 176-14E 29-13N 170-10E 28-28N 164-59E 26-39N 156-15E 23-28N 144-48E. CANCEL THIS MSG 041933Z OCT.

    Space debris →
  3. NAVAREA XI 424/26 · Derelicts · South China Sea2026-09-22 · in force

    …M/V MSC HERMES 3, 213 METRE LONG, ADRIFT IN VICINITY OF 11-45N 112-15E ON 220820Z SEP. CANCEL THIS MSG 250820Z SEP.

    Abandoned vessel, M/V msc hermes 3, 213 metre long, adrift in vicinity of 11-45N 112-15E on 220820Z sep →
  4. HYDROPAC 2712/26 · Exercises · Arabian Sea2026-09-18 · in force

    …064-27.83E, 25-12.00N 064-49.00E, 25-03.83N 064-49.00E, 25-03.83N 064-27.83E. 2. CANCEL THIS MSG 261300Z SEP 26.

    Hazardous operations 0300Z to 1200Z daily 25 and 26 sep in area bound by 25-12.00N 064-27.83E, 25-12.00N… →
  5. HYDROPAC 2709/26 · Exercises · Bay of Bengal2026-09-18 · in force

    …082-21.60E, 17-06.00N 082-26.00E, 17-00.50N 082-20.00E, 17-00.50N 082-17.10E. 2. CANCEL THIS MSG 241300Z SEP 26.

    Hazardous operations 0700Z to 1200Z daily 22 thru 24 sep in area bound by 17-06.00N 082-21.60E, 17-06.00N… →
  6. HYDROPAC 2707/26 · Exercises · Bay of Bengal2026-09-18 · in force

    …080-46.00E, 12-59.00N 080-46.00E, 12-59.00N 081-26.00E, 12-49.00N 081-26.00E. 2. CANCEL THIS MSG 241230Z SEP 26.

    Hazardous operations 0130Z to 1130Z daily 21 thru 24 sep in area bound by 12-49.00N 080-46.00E, 12-59.00N… →

How it reads in recent messages

  1. HYDROARC 251/26 · Icebergs · Laptev Sea2026-09-23

    …SEP IN: A. 77-06.70N 112-00.30E. B. 77-21.10N 109-24.50E. C. 76-39.50N 122-28.70E. 2. CANCEL THIS MSG 261419Z SEP 26.

    Icebergs reported at 230900Z sep in: a. 77-06.70N 112-00.30E →
  2. HYDROPAC 2760/26 · Exercises · Arabian Sea2026-09-23

    …072-27.00E, 20-26.00N 072-40.00E, 20-40.00N 072-40.00E, 20-40.00N 072-27.00E. 2. CANCEL THIS MSG 251230Z SEP 26.

    Hazardous operations 250230Z to 251130Z sep in area bound by 20-26.00N 072-27.00E, 20-26.00N 072-40.00E,… →
  3. NAVAREA XII 657/26 · Missiles2026-09-23

    …164-59.00E, 26-39.00N 156-15.00E, 23-28.00N 144-48.00E. 2. CANCEL NAVAREA XII 655/26. 3. CANCEL THIS MSG 041933Z OCT 26.

    Hazardous operations, space debris 1427Z to 1833Z daily 28 sep thru 04 oct in area bound by 23-55.00N… →
  4. HYDROPAC 2761/26 · Missiles2026-09-23

    …164-59.00E, 26-39.00N 156-15.00E, 23-28.00N 144-48.00E. 2. CANCEL HYDROPAC 2749/26. 3. CANCEL THIS MSG 041933Z OCT 26.

    Hazardous operations, space debris 1427Z to 1833Z daily 28 sep thru 04 oct in area bound by 23-55.00N… →
  5. HYDROPAC 2759/26 · Exercises · Laccadive Sea2026-09-23

    …075-11.00E, 09-35.00N 075-27.00E, 09-50.00N 075-27.00E, 09-50.00N 075-11.00E. 2. CANCEL THIS MSG 241830Z SEP 26.

    Hazardous operations 241330Z to 241730Z sep in area bound by 09-35.00N 075-11.00E, 09-35.00N 075-27.00E,… →
  6. HYDROPAC 2758/26 · Exercises · Bay of Bengal2026-09-23

    …085-29.95E, 18-45.00N 085-24.21E, 18-36.50N 085-10.10E, 18-33.61N 084-53.74E. 2. CANCEL THIS MSG 251929Z SEP 26.

    Hazardous operations in progress until 251829Z sep in area bound by 19-14.60N 084-53.70E, 19-07.39N… →

Earliest in the archive

  1. HYDROPAC 481/93 · Cable ops · Japan Sea1993-06-02

    …36-02.6N 133-07.3E, 36-02.8N 133-06.8E, 36-03.3N 133-06.6E 36-03.4N 133-06.2E. 2. CANCEL THIS MSG 11 JUL.

    Underwater cable operations in progress thru 10 jul along trackline joining 35-33.0N 133-02.0E, 35-33.3N… →

Often in the same message

Related terms

Cancellation reference
A line that cancels an earlier warning by its number, such as CANCEL HYDROLANT 1085/12.
Date-time group (DTG)
A compact UTC timestamp — day, hour and minute followed by Z — such as 201500Z for the 20th at 15:00 UTC.
In force
Currently valid: broadcast and not yet cancelled.
Until further notice
The operation or danger has no scheduled end; the warning stays in force until a later message cancels it.

Counts cover the messages in this archive that use the term, recounted 2026-09-24; see coverage for what is collected and since when. Not for navigation — follow official NAVAREA and coastal broadcasts.