Based on the same-named book by Ooshiro Tatsuhiro.

A documentary anime retelling the shipwreck of the freight boat Tsushima Maru, which was carrying a class of schoolchildren home in July 1944 when it was attacked and sunk by an American submarine. Produced by the surviving family members of the Tsushima Maru. A highly realistic and carefully crafted film in which the realism is thrown into contrast by the deformed character designs by Kiyomizu Kazutoshi.

(Source: pelleas.net)