Spc. Simran Lamba is the first turban-wearing Sikh in 30 years to be enlisted in the US Army and go through basic training:

The 26-year-old native of New Delhi, India, says it had been a childhood dream to become a soldier. He was permitted to wear unshorn hair and a turban under a special accommodation. The exemption applies to an Army policy that effectively prevented Sikhs from enlisting since 1984.

Recently, turban-wearing Sikhs have broken down barriers when it has come to joining the US military – particularly after 1984 when religious articles of faith were no longer acceptable.  Earlier this year, Captains Tejdeep Singh Rattan and Kamaljeet Singh Kalsi were given exemptions to join the US Army as officers with their turbans and beards intact.

A good article documenting the recent history of Sikhs in the US military is available on the US Army website.