Possible Clues:

• Firm
• 50% of dirigibles are of this construction
• Outfit I had found to be unyielding
• Clear about soldier standing thus to attention
• Stiff attire - notion half forgotten
• Arrangement of sails etc. I had put in stern
• One gets stiff in the grid
• Hard to give doctor passport, perhaps
• Fake papers fixed
• I'll confront soldier in middle of road, unwilling to move