Model of the first Magnetic Mine assembled at Cambridge June 1918.
The whole of the staff on this work were 500 Girton College girls.
The cylinder was filled with oil in which the magnetic field was immersed, the same supported by the gimbals in the centre of the mine.
The signature on the box is Proff J C McLellan of Toronto University, one of the first responsible for the development.
The star denotes the class which has been set to operate ; No1 30ft to No5 250ft.
At the time of my connection with this development five magnetic mines had been made by hand, but the constant testing had destroyed their practical value. I decided that the best thing to do would be to make 200 and test them, this was done in 2/3 months. Conclusions were reached and mines were put into service during the summer of 1918 with great success.