Reports in The Stage of an ‘American invasion in the theatre’ and the New Statesman writing of ‘our Americanized theatre’ expressed widely shared fears that transatlantic values were adversely affecting the British theatre in the wake of the First World War. In this article, Paul Marshall examines the strategies employed by the Lord Chamberlain's Office as it carried out its duties of censorship in dealing with plays from or about the United States. The Censor perceived it as his duty to defend public morals from elements that would threaten and challenge the values associated with ‘Englishness’, and, drawing on the Lord Chamberlain's Correspondence now available in the British Library, Paul Marshall explores how the Lord Chamberlain of the time, Lord Cromer, his readers, and his advisory board viewed the threat of the American ‘invasion’ – their shared values, sometimes disputed verdicts, and the formal and informal influences that could be brought to bear upon them. Five ‘case studies’ look at their attitudes to particular plays about and from the USA. Paul Marshall presently teaches history at Bromley High School, Kent, having studied for an MA in Text and Performance Studies at King's College and RADA.