A drum line brought the letters to the altar.
Members of the congregation of the House of Hope were dressed in red, white and blue for the occasion.
They wrote 25,000 letters.
2010 marks the 25th anniversary of the church, and leaders wanted to do something big that involved the number 25.
5,000 people attend the mega-church every Sunday, and it took them five weeks to complete the project.
"While you are there abroad defending that flag, know that the people of the United States are proud of you," said Rev. James Meeks of House of Hope.
The letters will be sent to servicemen and servicewomen in Iraq and Afghanistan.