IMHO, strength training plays a vital role in injury prevention and durability. Now, obviously I'm not a Special Forces soldier, so my opinion is based on what I experienced in the TACP pipeline. We do a fair amount of rucking ourselves and I think all the squatting, deadlifting, cleans, etc. helped me stay injury free and recovering better than some others I went through with. Not only that, but APFT focused fitness won't give you the strength to hoist a 200# dude wearing kit onto your shoulder and move out. You definitely have to have the right balance, but there are several programs that do. These programs are discussed in detail in threads in the Fitness forum if you're so inclined.