Will the Democrats ever win the military vote?

[Skill and Chance]

It's possible if we have a couple more interventionist Dem presidents and the GOP goes libertarian isolationist and stops sparing defense from the budget cuts.  Defense contractors would probably flip a few years earlier, so they will be the harbingers of any change in military voting IMO.

[Skill and Chance]

If the Democrat is a huge war hero

I mean like literally an Eisenhower or Grant type.

I really don't think we will ever have war heroes in the pre-1945 sense anymore.  Even containing and "winning" a hypothetical WWIII in the best case scenario would still mean losing >20% of the US population to nuclear warfare.  In a war with >50 million mostly civilian casualties even on the "winning" side, there are no heroes. 

The perception of winning or losing minor foreign conflicts can swing elections a bit (1968, 1980, 2002, 2004, 2006, maybe 2012) but there will probably never be another Ike or another 1944 election.