Spearhead is a new way to play Warhammer 40,000 that enables you to unleash exciting tank battles and daring breakthrough missions on the tabletop, bringing the full mechanised fury of the 41st Millennium to bear in your games. June's White Dwarf will contain the main part of the supplement, including new rules, missions and plenty of inspirational hobby advice. Alongside this, the Games Workshop website will feature additional material exclusively for registered members, such as details of how to assemble your Spearhead formations along with even more painting, modelling and collecting tips.
GW has posted a teaser about a new Warhammer 40K expansion that will be published in White Dwarf magazine in June. From their website: