Although Ramanujan had died nearly twenty years earlier, he had left a number of unpublished notebooks filled with theorems that Hardy and other mathematicians continued to study. Rankin did not work long on Ramanujan at this time, however, before World War II meant that he had to devote himself to war work.
Kahit Ramanujan had namatay halos dalawampung taon na mas maaga, siya ay nag-iwan ng bilang ng mga hindi inilathala notebooks napuno sa mga theorems na Hardy at iba pang mga mathematicians patuloy na pag-aaral. Rankin hindi gumagana ang haba sa Ramanujan sa oras na ito, gayunman, bago World War II sinadya na niya sa italaga ang sarili sa digmaan sa trabaho.