The phrase you’re hinting at points to a common crossword clue answer: GIJOE. Context and likely interpretation

• The clue “Soldier who can stand at attention indefinitely” is a playful way to reference a fictional or symbolic soldier who never “folds” under pressure.
• In many modern crossword contexts, the five-letter answer is GIJOE, playing on the well-known action figure and comic character G.I. Joe.

Direct answer
GIJOE If you’d like, I can explain the wordplay and how similar clues are typically constructed in NYT-style crosswords, or help with other five-letter soldiers-themed clues.