Bootcamp on Macbook Air: USB not possible?

Hi all,

I am currently trying to install Windows 7 on my Macbook Air (Late 2010, running with OS X 10.10.3). Since the macbook air doesn't have a DVD-drive, bootcamp should provide the possibility to create a bootable version of Windows on an USB-Drive, as far as I know.

My problem is, that bootcamp doesn't offer such an option on my mac. It just gives me the message that a DVD/CD-Drive is required to continue with the installation of Windows (which is not available on a Macbook Air).

I would be glad if someone could help me to solve this problem.

Kind regards,

Dennis