Related Clues:

• Cadence-call start
• One in the Army
• Advice to the overzealous
• One, to 65-Across?
• March beginning
• ''Take your time''
• Reminder to stay cool
• 'Heads up!'
• 'Gently'
• Marching start?
• March opener?
• ''Be careful''
• Drill sergeant's "one"
• Cadence-call syllable
• Drill instructor's syllable