Basic Training
In a lot of movies, the cast have to spend weeks and even months training for their roles. They are taught by some of the best teachers in the business, and this allows their characters to move and act properly in their specific situations. Sam was a shoe-in for army characters, since he already had extensive knowledge about the proper language, forms, and behaviours that were expected in the army. He needed far less training than other actors.
Small Roles
Don’t get this story wrong: Sam Elliot had to work his way through Hollywood to get to where he is today. At first, no one was very familiar with Elliot, and so he had to accept a lot of small roles before important people started taking notice of him. This wasn’t a big deal to Sam, since he had been fighting for this career ever since he had first shared his dream with his parents. He seemed to already know that it would be an uphill battle.