Possible Clues:

• Unable to be forced out of shape
• Hard to fake passport, perhaps?
• Falsify documentation for firm
• Firm hides soldier in shed
• Like a dirigible, vis-a-vis a blimp
• Harsh soldier's shut outside
• Equipment I had to make very firm
• Austere American soldier getting in free
• Like a zeppelin, as opposed to a blimp
• Firm's doctor with badge