Exercise Tiger was a real disaster, kept secret from families for decades. Morpurgo uses fiction to give these forgotten soldiers a human face.
Adolphus is treated differently because of his race. Lily finds this deeply unjust. Morpurgo presents racial segregation in the US Army honestly and critically.
The secrecy around Exercise Tiger meant families never knew the truth about how their loved ones died. Morpurgo argues that truth and memory are forms of justice.