The U.S. Navy is concerned about an increase in suicides among its submariners. There are only about 20,000 men qualified to service in the navy's nuclear subs. Last year, seven of them committed suicide. That's a rate of about 35 per 100,000 (the usual measure for such things.) The U.S. Army had a rate about a third of that. The entire navy has a suicide rate that is about the same as the army's (about ten per 100,000 uniformed personnel). In 2004, the suicide rate for submariners was 20 per 100,000.
While the numbers are small, they are seen as a possible indicator of morale, and other, problems. Submariners are carefully selected and intensively trained. Their work involves dealing with complex electronics, nuclear power plants and nuclear weapons, under intense conditions. The navy has long screened submariner candidates for psychological problems. The last thing you want on a nuclear boat is a crewman with psychological issues.
While the sudden "surge" in suicides involves a small number of people, and may just be a normal statistical blip, the navy has to double check and make sure there are not more widespread, underlying causes.