The soldiers were part of the Operation Tomodachi, which was such a tremendous help to the people in the disaster-affected areas in Tohoku in the early days of the earthquake/tsunami disaster in March last year. Unfortunately, the disaster also involved the nuclear accident, but at that time hardly anything about radiation exposure for the US soldiers, or SDF soldiers, or Japanese and international volunteers, were even mentioned in the news.
Asahi Shinbun reports that these soldiers were on board USS Ronald Reagan.
See, people in Japan, this is how much you should also sue TEPCO for - demanding US$10 million each (860 million yen), plus punitive damage of US$30 million. Add one or two zeros on your claim form.
The problem of course is that that money, or any money being demanded out of TEPCO, will eventually come from Japanese taxpayers' pockets, now and in the future. TEPCO is owned by the national government.
USS Ronald Reagan was in the Korean Peninsula region when the March 11, 2011 disaster struck. The carrier was diverted to Japan, and was used as a floating base off the coast of Sendai, Miyagi. From Wiki entry:
The ship departed for an Asian deployment on 2 February 2011. On 11 March 2011, Reagan was in the Korean peninsula region for a long-planned exercise off Korea, but was redirected towards Japan to provide support after the massive 2011 Tōhoku earthquake and tsunami. The ship, stationed off Sendai, was used as a floating refueling station for Japanese military and coast guard helicopters flying relief missions in the area. US Navy helicopters also flew relief missions from the carrier. On 14 March 2011, the ship was forced to relocate to avoid a radioactive plume from the Fukushima I nuclear accidents which had contaminated 17 crewmembers of three helicopter crews.[dead link] On 23 March, the Reagan's crew conducted a radiation decontamination operation to remove any further radiation hazards from the ship, which included scrubbing down any surface that could have been contaminated, including the flight deck and aircraft.
The report on March 14, 2011 about the ship relocating is here. It says the 17 helicopter crews were exposed to one month worth of background radiation, and they were on a relief mission to Sendai, Miyagi.
From BBC (12/27/2012; emphasis is mine):
Japan's Tepco sued by US sailors over radiation
Tokyo Electric Power Company (Tepco), owner of the crippled Fukushima Daiichi nuclear plant, has been sued by eight US sailors over radiation exposure.
They claim that Tepco lied about the threat posed by the leaks after the March 2011 earthquake and tsunami damaged the plant.
The soldiers were involved in relief operations after the natural disasters.
They have each sought $10m (£6m) in compensatory damages and $30m in punitive damages from Tepco.
The soldiers, who have filed the case in a US Federal Court in San Diego, also want Tepco to set up a $100m fund to pay for their medical expenses.
They have claimed that the utility provider created an impression that the level of radiation leaks from the nuclear plant did not pose any threat.
As a result, the sailors say they went to areas that were unsafe and were exposed to radiation.
When contacted by the BBC, Tepco acknowledged that it has been sued, but said that it had not received the actual complaint and so was not in a position to comment.
The lawsuit is the latest setback for Tepco which is already facing billions of dollars in compensation claims.
The radiation leaks resulted in thousands of people and businesses being evacuated from the areas surrounding the plant.
On Thursday, the firm said that it now expects the compensation costs to total at 3.24 trillion yen ($38bn; £23bn), up 697 billion yen from its earlier projection.
The firm has already received nearly 1tn yen in government aid.
The utility was, in effect, nationalised after the government took a 50.11% stake in the group in exchange for the capital injection.
In September this year, the US Department of Defense set up a special registry for the participants of the Operation Tomodachi.