Along with that, they have their June books up for pre-order, including books on the SR71 Blackbird, Waterloo, Confederate and Union cavalry, and Spetsnaz soldiers.
From the announcement:
Get 20% off Campaign Books
Until the end of March you can get 20% off all of our Campaign books - as well as 20% off their eBook counterparts.
In addition to this, Gold and Silver members will have their own discounts added to this offer.