查時間點：after the flood, not before it.

The deployment of approximately 500 personnel—including the Texas National Guard—happened during and immediately after the flood, not before it.

Here's how it unfolded:

• Flash flooding began in the early hours of July 4, following storm activity late on July 3 yahoo.com+15en.wikipedia.org+15yahoo.com+15yahoo.com+1en.wikipedia.org+1.

• The blazing-waters event overwhelmed Camp Mystic at around 4:00?a.m. CDT on July 4 apnews.com+14en.wikipedia.org+14en.wikipedia.org+14.

• Once the flood hit, search-and-rescue operations sprang into action. Reports from July 4?5 indicate that about 500 responders, including National Guard troops, Coast Guard personnel, helicopters, drones, and dive teams, were deployed to aid survivors and locate missing people nypost.com.

So, in summary:

• Timing: The deployment occurred during and after the flash flood on the morning of July 4, not beforehand.

• Before the flood, authorities had issued weather alerts and watches (e.g., on July 3), and the camp had only received approval of its emergency plan—but major personnel deployments came in response to the disaster itself, not pre?positioned pre?flood.