Asides from the pertinent information in BelDion's writeup, Marcus Island was jointly occupied by both Japan and the U.S. until some point in the mid-to-late eighties. However, the U.S. half was still recognized Japanese territory merely under lease to the United States Government.
The Japanese presence on the island was manifested in an observation station maintained by the Japanese Meterological Association, while the American presence was LORSTA Marcus--a LORAN station maintained, operated, and being under the full jurisdiction of the United States Coast Guard, Far East Section.
Marcus Island is extremely removed from society, being but a tiny, slightly darker blue dot in the light blue ocean of the average classroom globe. It lays just above the equator and just to the west of the International Date Line. Communication with the outside world was maintained through ham radio, and C-130's maintained a supply line through monthly to bi-monthly visits. There was also a satellite television feed that found itself sometimes dependant on whether or not a television satellite was actually passing over the island. Listening to any sort of commercial radio was right out, unless you found yourself lucky enough to possess a short wave reciever.
It was also of note that Marcus was actually quite a heavily contested location during the island hopping strategies of World War II. The island is latticed with underground tunnels, bunkers, abandoned machine gun nests, ruined piers, and--more precariously--unexploded bombs and land mines.
Asides from the obvious war relics, there are three interesting Japanese landmarks on the island. The first of these is a small monument marking the southeastern-most point of the Japanese Empire. The second is a memorial to a failed Japanese settlement established there early on in the 20th century, or late 19th century (apparently the settlers were deposited on land, but the fresh water wasn't...). Thirdly, Marcus was actually graced with the highest free-standing structure in all of Japan, as the Coast Guard's LORAN station transmitting tower was over 1,000 ft. tall.
That particular tower was detonated in early 1986 to make way for a new tower.
The island itself was formed by coral reef growth formed on top of a submerged and dormant volcano. As a result of this, the actual island is surrounded by a sort of "apron" of reef--providing for a fairly shallow descent from the beaches--before rising sharply to form a wall, which surrounds the apron, and then finally dropping off into the near-impenetrable nothingness of the central Pacific Ocean. The reef itself, and especially the outermost coral wall, provided for a natural defense against beach landings and amphibious craft. The Japanese actually blasted a rectangular channel in the wall so their own ships could dock and depart.
Whereas I am not particularly sure about the Japanese weather crews, the USCG personnel were assigned to the station for one year tours. As part of this assignment, the crewmen were also granted four weeks of shore leave with the option of taking it all at once or in two weeks halves. This provision was obviously granted to keep the crewmen from going insane. The almost mythical C-130s charged with carrying a departing crewmen along with the rest of the manifest were called "Freedom Flights."
Whereas some people would immediately draw names such as Siberia, or the summit of Mt. Everest, or even Antarctica, I would personally have to say that I believe Marcus Island is one of the most isolated places on the earth--if not the most isolated. The island is very small, and surrounded by nothing but the flat mirror-plane of the Pacific in all directions. That plane extends for thousands of miles until finally reaching even a semblance of populated landmass. Though the island bears many trees--and a limited amount of fauna (including a gawdawfully huge brand of arachnid called a "Fillmore" after a USCG cook who kept one as a pet)--the soil is mostly a kind of semi-barren coral sand which can't support much else.
The photos I have seen of the island belie a certain beauty and a sense of tropical heaven. However, after a week or so of looking at the lovely plants I feel I would get over the tropical novelty and feel lonelier than I ever had before.
Had things gone poorly for humanity in the 1980's, this probably would have been one of the last places standing. Most likely it would have been the only place standing.
The Japanese name for the island--and forgive me for most likely butchering the spelling here--is "Minami Tori Shima" which translates to "South Bird Island."
Also, Marcus Island was the assigned duty station for my father from April 1985 to April 1986. As an MK1 it was his duty to keep the massive generators that ran everything from crapping out and destroying navigation over a vast section of the Pacific. So, it should be noted that all of my information is about that old. The American lease, though, has by now run out--and there were no plans by the American Government to renew.