http://en.wikipedia.org/wiki/Inmarsat
Briefly, INMARSAT is a private British company that communicates with vessels, air and sea, via satellite. Their original market was ocean going vessels, hence the “International Maritime Satellite” (IMO is the International Maritime Organization, a quasi-governmental body making recommendations for laws and regulations about the operation of vessels in international trade.) I do not know if INMARSAT is affiliated with IMO.
The head of the company said it was orig founded by the UN or something.