General surg is the way to go to get to most types of trauma. I believe the fellowship is 1-2 years depending upon the program. I'm not too sure about how competative they are. Gen Surg programs are at least 5 years now, almost all academic programs are 6.
However, if you join the army and go into Gen Surg, you may be able to bypass the fellowship, as trauma is not an accredited fellowship anyways. The US army is in such a dire need for shock trauma surgeons that no matter what kind of surgeon you are, they send you to do trauma. There was a great article about this in the NEJM by Atul Gawande (author of Complications: A surgeon's notes on an imperfect science), in which the author describes urologists, ENT, and other non general surgeons being called to duty and working as trauma surgeons too. If you end up joining up, I'm sure finishing either your civilian residency (if they let you do one) or military residency in general surgery, you will be put to work as a trauma surgeon even in spite of your wishes to do a fellowship.
Battlefield trauma as discusssed in the above article is very different from civilian trauma, and its not the gun shot wounds that are the problem. Its the IUD concussion injuries, injuries that injure areas unprotected by body armor (like the armpit), and such. This type of trauma is very different, and as a surgeon, you'll be working to just save their life, then hopefully their limb and stabilize them enough to be transported off of the battlefield hospital.
By the way, there are also other types of trauma surgeons such as Neuro as well as Ortho, however, again, if you are in the army, maybe the Neuro surgeon would not, but I'm sure the Ortho surgeon and everyone else would be doing shock trauma.
Hope this helps.
sscooterguy