Hato yo: Hiroshima no Sora wo
Type: OVA, Episodes: 1
Aired: 1999
Source: Unknown
Rating: G - All Ages
Synopsis:
Based on a book of the same name. 

An anime about the atomic bombing of Hiroshima. The focus is a middle school boy who kept and bred carrier pigeons. While he was out of the city training them, the bomb dropped. Both he and the pigeon desperately tried to find their mother and child respectively in the chaos.