Ballista Media has produced a number of  informative nonfiction apps for middle and high school students. Like its Timeline Battle Castle app, Somme 100 is based on a British television series hosted by Dan Snow.  Celeste Steward reviews it below. The Battle of the Somme, also known as the Somme Offensive is commemorated in an app marking its centennial. Fought by the British and French troops against the German Empire, the Somme Offensive launched on July 1, 1916. British armies lost nearly 60,000 men on the first day alone, making it the bloodiest battle of First World War. By the end of the five-month campaign, the Allied and Central Forces suffered more than one million casualties. Ballista Media’sSomme 100 (iOS; Android; both Free; Gr 9 Up) contains more than 200 archival black-and-white labeled photos, fascinating period film clips, videos, historical and contemporary commentary, and map entries. This compelling package, commissioned by the Royal British Legion, features videos of television historian Dan Snow's discussing the key battles of the campaign (and related topics) from the sites, interspersed with period film footage. While the app is an overview of the offensive, it packs a significant amount of information into a well-organized framework. From the home page, a three-tiered, illustrated "Battle Timeline" lays the groundwork for the events leading up to the event along with a multimedia sections on  the "Voices of War" and the "Battle Day by Day." Viewers can switch between levels using the navigation menu. The "Map of the Somme" offers a geographical view of battles by date while the "Battle of the Somme" provides background information in a multilayered arrangement. Users may browse information there by events, battles, or dates or topic. An Internet connection is required for the audio and video portions. "Animated Battle Maps" provides an illustrated view of the largest movements of the campaign by the hour(s), day, or month, while the "Pals Battalions" page offers information on a selection of the many British volunteer soldier brigades. Of particular note are the diary entries and audio recordings of the men who fought in the trenches, making this a truly superb resource for students.The Somme 100 app is a must-have for military history buffs and an excellent springboard for further research on the Great War.—Celeste Steward, San Leandro Public Library, CA