Possible Clues:

• Join those marching across the open manhole?
• Army order to form a line - don't collapse!
• Join the ranks, darling!
• 'Take one's place in a military line (4,2)'
• Army order to take place in formation
• Military order to join formation
• Almost collapsing, get on parade
• Military order - take place in formation
• Sergeant's order for part of fish containing everything
• Boot-camp command