How do you address 2nd Lt and his wife in letter?

In a letter addressing a 2nd Lieutenant and his wife, you would typically start with "Dear 2nd Lieutenant [Last Name] and Mrs. [Last Name]." If you know the wife's first name, you can use "Dear 2nd Lieutenant [Last Name] and [First Name]," keeping the tone respectful and formal. Always ensure to maintain a polite and courteous tone throughout the letter.