Blanche (on the far right in the photo) was born in Hammersmith, London on 21 December 1873. Her parents were Sir John Isaac Thornycroft and Blanche Ada Thornycroft (nee Coules). Blanche had four sisters Edith Alice, Mary Beatrix, Ada Francis and Eldred Elizabeth. Blanche also had two brothers, John Edward Thornycroft who followed his father as the governing director and chairman of John I. Thornycroft and Co., Ltd. and Isaac Thomas (Tom) Thornycroft also worked in the firm until 1934. As far as it has been possible to discover, of the women in the Thornycroft family only Blanche seems to have been involved in the family firm, although there is no record of her being salaried nor of any other form of payment to her. It is also unclear where she picked up her knowledge of mathematics and engineering as there is no record of any formal education at university level.
Blanche grew up on the banks of the Thames at the family home in Chiswick, her father having established a boatyard there in 1866, and so boats would have been part of her life. The family also had a home Steyne Wood House at Bembridge on the Isle of Wight where scaled models of boat hulls could be tested in a pond. In 1909 John I. Thornycroft purchased land nearby to Steyne Wood House and commissioned the design and building of a new purpose built indoor test tank which was finished in 1910.
Blanche’s position as an assistant to her father seems to have been informal as there is no record of her being part of the family firm. However, there was external recognition, and validation of her role as an engineer. The professional body which ‘governed’ Naval Architecture was in 1919 known as the Institution of Naval Architects (INA). The admission of women into its ranks seems to have been prompted by the work done by women in the field of ship design during the First World War and in late 1918 a referendum was held among its members, which asked if women should be admitted on the same terms as men. In April 1919 at its annual meeting the decision was taken by the institute to allow it. By the 9th May 1919 John I. Thornycroft had submitted a cheque on behalf of his daughter Blanche and by the 19th May her diploma of membership had been received.
Blanche also involved herself in wider life on the Isle of Wight. Along with her mother she helped found the Bembridge Nursing Association and she was a member of the Bembridge Sailing Club. Blanche also had an interest in botany and was a council member of the Isle of Wight Natural History and Archaeology Society.
Information collected for this topic page was through the ARHC funded project ‘Business, government and the workplace: John I. Thornycroft & Company Limited, and the Great War', and research conducted by Roy Edwards, University of Southampton and Keith Harcourt