I don't know about the WWII case, but in countries like the UK where it is legal to be buried at sea there are regulations about where you can perform the ceremony specifically because bodies do drift: https://www.bbc.com/news/world-europe-guernsey-24224570

Although the article mentions that this is the first time it's happened in 25 years, note that only about a dozen people every year choose to be buried in this way: https://www.bbc.com/news/uk-england-38210497

It's definitely a thing even without combat areas: https://en.m.wikipedia.org/wiki/Salish_Sea_human_foot_discov...

So if you scale up from the relatively small numbers of people who die (and whose bodies aren't recovered) by accident or suicide near/in water, it's probably reasonable to expect a lot more of this. Maybe your idea is workable if you go far enough out that any detached remnants are grabbed by the big oceanic gyres.

Or if the people buried at sea aren’t wearing anything too buoyant, such as sneakers.