This question hones in on your ambition: an interviewer who asks this wants to know what you're attempting to achieve. Discuss your plans for the future so that your personal ambition benefits the company.
Don't just answer this question by saying, "because I'm awesome," or a wordy, detailed version thereof. This is an opportunity to talk about what makes you the right candidate for the position. This requires knowing what the employer is looking for, and then matching your skills and experience to it.
-“If hired, I plan to staying here as long as possible. I can't predict the future, but I can tell you that when you hire me, that no matter how long my tenure is here, you're going to get a great employee who works hard for you.“
Professional, but there's still fun here or there between you and you battles. It is serious, though. Everything you're doing is preparing for combat, so you need to take it seriously.
I'm sure you would agree that it's an employer's market. Sometimes you have to make sacrifices to move up on the career ladder. I've taken all of my experiences in the places I've lived and apply them to every facet of my career and being so mobile has definitely improved my ability to adapt and learn quickly.
Try to postpone this question until you receive a job offer. Prepare by knowing the going rate in your area. A good resource is the U.S. Bureau of Labor Statistics. If you don't know the range and the interviewer persists, reply, What salary range are you working with? The interviewer may very well tell you.
Whilst this question should be generally easy to answer, it does end up throwing many applicants. Most people who apply to join the Army will do little or no preparation for Officer Initial Training until they have received confirmation that they have passed the AOSB. However, if you can show the Army Careers Advisor that you are already preparing for training then this will impress them. Here is a sample response to assist you.
All services have overseas opportunities. Overseas service is often considered a "square to fill" for advancement. Ask your recruiter.
I was a 19 Kilo Armored Crewman. Primary duties when I got into the job was preventive maintenance on the vehicle, cleanliness, loading the main gun, and being the gunner for the crew served 240 Bravo.
This is a reverse invitation to promote your skills. Do it with an answer that puts you in a good light. For example, I tend to be too detail-oriented, but I work hard to control that. Keep it simple - and smile.