I like the idea of number 2, although you'd have to make it unique somehow. Time Travel stories have been done before. Maybe add a little twist to it, an alternate reality time travel? Let's say he's back in Civil War america and the south wins so he tries to "fix" history or something like that? Definitely wouldn't be easy, but it might help you a bit as no one can be sure what would happen in an alternate reality, so you could definitely play around with it. Just my 2 cents.
My thought is to start brainstorming/writing on all three and decide which idea you would make into the best story.
#2 idea. Similar to how John Carter ended up on Mars, you could have a Troop in afganistan with his m4 and ammo, end up in a Napoleonic battle. That would be fun.
It's been done...there was a crappy movie made a while back ('70s-'80s) about a bunch of US Vietnam-era soldiers being transported back in time to the American Revolution.
It's been done to death. There was one about that US Aircraft Carrier in the Pacific being transported back to right before the Japanese attack on Pearl Harbour and then there was the Philadelphia Project and that one with Mel Gibson.
Oh yeah, forgot all about "The Final Countdown"...
Stephen King did a great job last year with 11/22/63.
1. Mission Impossible and the dozens of other shows that have copied it.
2. Back to the Future and the millions of other similar stories. Heck, between the Time Traveller's wife and that new movie with Bruce Willis and that other guy as a time travelling hitman, its still being done to death.
3. That's a pretty broad idea.
In this case it would be a warewolf...
And lots of T&A, action, and car chases. Worked for Ian Flemming (and pretty much everything ever written for guys).