A discussion on the structural design problems associated with the design of the pressure hulls of submarines in view of the increasing depth requirements that were being specified at the time [1933]. The circular form was advocated in preference to a combination of incomplete circles, such as the Flamm "Shamrock" section. A number of formulae were quoted or advanced for calculating the stresses and it appeared that the axial stress generally exceeded the tangential value. Failure was usually due to instability of form and not to excessive fibre stress. A rather startling and paradoxical conclusion was that the presence of a bulkhead might increase and not decrease the local stress in the vicinity.