11 May 2009
Quoting RECORD OF PRELIMINARY HEARING UNDER ARTICLE 32
Robert Bowdrie Bergdahl -- or Bowe Bergdahl as he wished to be known enlisted in the Army on 12 June 2008. He completes basic training and AIT at the end of October 2008 and reports to Blackfoot Company, 1st of the 501st Parachute Infantry Regiment at Fort Richardson, Alaska. Here he’s assigned to 2nd Platoon. 2nd Platoon is on its way to NTC -- or the National Training Center at Fort Irwin, California, for training. After the exercise, 2nd Platoon and the accused return home for Christmas and block leave; and in March of 2009, 1st of the 501st deploys to Paktika Province in Afghanistan. The accused deploys with his unit, although he’s several weeks behind the main body due to an infection in his heel. He arrives in Afghanistan on 11 May 2009, and he joins his unit in the rotation schedule between Forward Operating Base Sharana and Observation Post Mest in Afghanistan.
Also, according to congressional testimony of Cody Herbert Full, Bergdahl's roommate:
In March 2009 our Brigade deployed to Afghanistan but Bergdahl did not make the deployment with us. He had gotten a staph infection and would not make it until May 2009.
(alternative official US link to Cody Herbert Full's testimony)
Additionally, Bergdahl posted to facebook with the user name "Wandering Monk". His last post was 22 May 2009 and described a mission in Afghanistan that took fived days.