Howlett then presided over the recording of a further hit single, "Souvenir", co-written by Cooper & Humphreys. It ushered in a lush choral electronic sound. The song also became OMD's biggest UK hit to date. In November 1981, their most commercially successful album was released in the UK and Europe – "Architecture & Morality". The group went into the studio with Richard Mainwaring producing. Cooper then temporarily dropped out and was replaced by Mike Douglas, but this change was reversed by the time the album was released and a tour followed. The album's sound saw OMD's original synth-pop sound augmented by the Mellotron, an instrument previously associated with prog rock bands. They used it to add very atmospheric swatches of string, choir, and other sounds to their palette. Two more hit singles "Joan of Arc" and "Maid of Orleans" (which became the biggest-selling single of 1982 in Germany) were on the album. "Joan of Arc" and "Maid of Orleans" were originally both titled "Joan of Arc"; the name of the latter single was changed at the insistence of the publishers and to avoid confusion. It became "Joan of Arc (Maid of Orleans)" and later simply "Maid of Orleans".