[tz] Timezone history for some Pacific Islands.

Phake Nick c933103 at gmail.com
Sat Oct 27 13:41:02 UTC 2018

>From a Japanese wiki site https://wiki.suikawiki.org/n/南洋群島の標準時 there are
some time change history about Pacific Islands that are not included in the
tz database. Mainly, the history of time used in those islands during,
before and after Japanese administration, and also DST used in Guam during
1960s and 1970s.

For "Southern Islands" (modern region of Mariana + Palau + Federation of
Micronesia + Marshall Islands):
* A 1906 Japanese magazine shown the Caroline Islands and Mariana Islands
who was occupied by Germany at the time as GMT+10, together with the like
of German New Guinea. However there is a marking saying it have not been
implemented (yet). No further information after that were found.
* Japan invaded those islands in 1914, and records shows that they were
instructed to use JST at the time
* 1915 January telecommunication record on the Jaluit Atoll shows they use
the meridian of 170E as standard time (GMT+11:20), which is similar to the
longitude of the atoll.
* 1915 February record say the 170E standard time is to be used until
February 9 noon, and after February 9 noon they are to use JST.
* However these are time used within the Japanese Military at the time and
probably does not reflect the time used by local resident at the time (that
is if they keep their own time back then)
* In January 1919 the occupying force issued a command that split the area
into three different timezone with meridian of 135E, 150E, 165E (JST+0, +1,
+2), and the command was to become effective from February 1 of the same
year. Despite the target of the command is still only for the occupying
force itself, further publication have described the time as the standard
time for the occupied area and thus it can probably be seen as such.
** Area that use meridian of 135E: Palau and Yap civil administration area
(Southern Islands Western Standard Time)
** Area that use meridian of 150E: Truk(Chuuk) and Saipan civil
administration area (Southern Islands Central Standard Time)
** Area that use meridian of 165E: Ponape(Pohnpei) and Jaluit civil
administration area. (Southern Islands Eastern Standard Time)
** In the next few years Japanese occupation of those islands have been
formalized via League of Nation Mandate (South Pacific Mandate) and formal
governance structure have been established, these district [become
subprefectures] and timezone classification have been inherited as standard
time of the area.
** Saipan subprefecture include Mariana islands (exclude Guam which was
occupied by America at the time), Palau and Yap subprefecture rule the
Western Caroline Islands with 137E longitude as border, Truk and Ponape
subprefecture rule the Eastern Caroline Islands with 154E as border, Ponape
subprefecture also rule part of Marshall Islands to the west of 164E
starting from (1918?) and Jalnuit subprefecture rule the rest of the
Marshall Islands.
* And then in year 1937, an announcement was made to change the time in the
area into 2 timezones:
** Area that use meridian of 135E: area administered by Palau, Yap and
Saipan subprefecture (Southern Islands Western Standard Time)
** Area that use meridian of 150E: area administered by Truk(Chuuk),
Ponape(Pohnpei) and Jaluit subprefecture (Southern Islands Eastern Standard
* Another announcement issued in 1941 say that on April 1 that year,
standard time of the Southern Islands would be changed to use the meridian
of 135E (GMT+9), and thus abolishing timezone different within the area.
* Then Pacific theater of WWII started and Japan slowly lose control on the
island. The webpage I linked above contain no information during this
period of time. Guam Island was briefly annexed by Japan during this period
of time [year 1941-1944], however there are no detailed information about
what time it use during that period. It would probably be reasonable to
assume Guam use GMT+9 during that period of time like the surrounding area.
* After the end of WWII, in 1946 February, a document written by the
(former?) Japanese military personnel describe there are 3 hours time
different between Caroline islands time/Wake island time and the Chungking
time, which would mean the time being used there at the time was GMT+10.
* After that, the area become Trust Territories of the Pacific Islands
under American administration from year 1947. The site listed some
American/International books/maps/publications about time used in those
area during this period of time but they doesn't seems to be reliable
information so it would be the best if someone know where can more reliable
information can be found.
* The site also pointed out that currently tzdata say Pacific/Kwajalein
switched from GMT+11 to GMT-12 in 1969 October without explanation, however
an 1993 article from NYT say it synchorized its day with US mainland about
40 years ago and thus the switch should occur at around 1950s instead.
* Also, the NYT article linked in that website say the jump from GMT-12 to
GMT+12 in year 1993 skipped Saturday that day, however the comment in tz
database from that year say it skipped Friday. That seems to be an
inconsistency that should be investigated, and the comment should probably
be annotated accordingly if the comment was not accurate

ANd then additional note for Bonin Islands:
While not part of the Southern Islands, in the period of time during
1952-1968, Bonin Islands were placed under American administration. It
would probably be worth investigating whether they're following the
Japanese time or the Mariana time or some other time standard at the time.

And then for Guam:
* Currently tz database say Guam stopped using local mean time at 1901 but
a 1902 earthquake report on Guam seems to be using LMT in the report when
compares to the time the earthquake recorded on the Philippines (the site
note that it take times for earthquake wave to transmit and thus the time
different between records in different place would not be identical to the
time different)
** The site say Shanks used 1901 end date for LMT time for a number of
places around the world, probably using them as placeholder. Maybe those
1901 end date should be nuked from tz database?
* A Japanese magazine in 1906 say Guam's time is "1.5 hours earlier than
Japan" and "use 145 degree E meridian" which are contradictory to each
other as 145E meridian mean GMT+9:40 and that is not 1.5 hours earlier than
* And then there are some different records about Guam used GMT+9:30 at the
time but each of those documents seems to give different transition time
for when they give up :30 time different and move to GMT+10. But it most
likely occurred before 1927 as a map published by US Navy that year shows
Guam as using GMT+10, which appears to be credible as Guam was under US
Military administration at the time.
* As mentioned above, Guam was invaded by Japan during year 1941-1944. It's
unclear about did they shifted the clock to match the surrounding islands
during this period of time.
* Then in year 1959 there's a daylight saving time act passed for Guam.
There is a table on the site that include list an link to time and order
for implementation and cancellation of DST at Guam but the implementation
time seems to be all over the place according to the list. The last time
the DST was implemented in Guam according to the table seems to be 1977
although I am not sure about the completeness of the table. If so then
maybe a new zone for CNI would need to be created as it's after 1970 and
the DST should be applicable to Guam only?
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