I recommend that any plans for deferral not be mentioned anywhere in a primary or secondary application (or in an interview unless you are asked a question that would require that you indicate such an intent). Go through the normal application process. If your plans for service solidify after you have gained an acceptance, you may request deferral from your first-choice school. If that school is not inclined to grant a deferral, then ask the second-choice school. I am happy to discuss this recommendation on a more individual level.