Your right 2006. Looks like 2005 was when the decision was made, and feb 24, 2006 was when it was offical

http://www.defenseindustrydaily.com/...-marsoc-03793/
Who was missing from this picture? The Marines. Why? Because to the Marines, every Marine is special. After all, what higher honor could there possibly be than to say you were a US Marine? None. Which is why the USMC had Force Recon personnel, and whole Marine Expeditionary Unit – Special Operations Capable formations. They had no special forces. Until November 2005, when the US Marines agreed to stand up MARSOC with 2,500 Marine special forces – even as they managed to remain true to their credo. MARSOC was formally established on February 24/06.