The stories told here about
exposure to chemical insults and presumed association with health problems in the following generation, would all once have been dismissed. However, there is now a known mechanism by which this may happen - epigenetic change.
There is actually relatively little genetic diversity between humans, in terms of which genes they have. What differs radically is which genes are switched on, and how active they are. In particular, this tends to be variable in the germ cells (ova and sperm), as this increases adaptivity to prevailing conditions in succeeding generations. So if one generation experiences famine, that switches on genes in the cells that then become the following generation, and they are more prone to putting on weight in different ways, are metabolically different, are prone to different diseases etc. This was first seen after World War 2, and many specific instances are now known; alcoholism and diabetes may be examples.
In Crohn's there are known specific sets or variants of genes (like NOD2) which are part of an inflammatory response to chemical and biological insults in the gut, and without which the disease process does not (so far as we know) happen. Since most pesticides, particularly of that era, were mutagenic - known to change DNA - and often teratogenic (caused fetal malformation) it isn't hard to see how they could create modifications to genes which would kick start the disease process in Crohn's, cancer, and who knows what else with an immunological component.
As regards exposure to Agent Orange on ships, I am pretty sure that when I first read up on it many years ago, I read of US Navy sailors suing after exposure to leaking barrels that they were handling; it stuck in my mind as being their very bad luck, being (so you might expect) safe from defoliants.
Agent Orange was originally discovered as a trace impurity in the manufacture of Tricholorophenol, which was then a ubiquitous hand cleanser and disinfectant in medical use. When certain types of cancers in the nursing profession rocketed, research highlighted 2,4T, as the associated impurity that caused this, and the manufacturing process changed; but actually it was 2,4,5 T and the associated dioxin that made Agent Orange so lethal, present in even smaller quantities, that were the real culprits. Once discovered, someone found a profitable use for these all too common "waste impurities" present in large quantities from the manufacturing of chlorinated compounds, so they did not have to be treated as toxic waste...and the rest is history.
I believe that to this day, the Triclosan found in antibacterial cleaning products is one molecular twist away from Agent Orange. Welcome to free market economics...