Letter from unidentified individual [?Dr Alwyn Crow, Director and Controller of Projectile Development] (Great Westminster House, Horseferry Road, London) to F A Lindemann [later 1st Lord Cherwell, Prime Minister's Personal Assistant] (Offices of the War Cabinet, Great George Street) on the programme for a demonstration of anti-aircraft weaponry for WSC on 11 April at Aberporth [Cardigan, Wales]. [annotated copy].