Last month, the Institute of Medicine (IOM) released a report that looked at possible connections between Agent Orange and Blue Water Navy Veterans who served in Vietnam. The report concluded that there isn't enough information available to justify tying a presumption of Agent Orange exposure to Blue Water service. But, like a lot of medical reports, if you're not an expert, the results can be a little hard to interpret-to figure out what it actually means for Veterans.
Blue Water Navy Vietnam Veterans are those who served aboard deep-water U.S. Navy vessels, but did not dock or set foot on land in Vietnam. On the other hand, Brown Water Navy Vietnam Veterans served on vessels that patrolled the inland shoals and waterways of the Republic of Vietnam.
With respect to Agent Orange, Brown Water Veterans who served in Vietnam during the war (and who have an illness which is presumed to be related to the herbicide) don't have to prove an association between their medical problems and their military service. There are 14 diseases that fall under this presumption, and they're referred to as presumptives.
Here's a little bit of a timeline: