Related Clues:

• Poet inspired by the Battle of Baltimore
• Song's harmonic center
• 'The Star-Spangled Banner' lyricist
• One of many on a custodian's ring
• B minor, e.g
• Caps Lock, e.g
• Instrumental
• Sandy islet
• One in, or on, a chain
• Fundamental, and a word that can follow the first parts of 20-, 31-, 41- and 52-Across
• Hotel desk handout
• One might be hidden under a mat
• Anthem writer Francis Scott ___
• Message-encrypting instructions
• Islet on a coral reef