§ Mr. Healey
As I explained on 18th October, we are still investigating these defects, but it is already clear that a fundamental factor affecting the extent and propagation of the cracks is the presence of non-metallic inclusions in the high strength steel used in building these boats, which was first ordered in 1957. We are taking steps to deal with the cracks by buying a quantity of one of the latest types of American steel. Two British firms are also beginning to produce steel-plate to the standards which we now know to be necessary, and this will be used for our purposes as soon as it can be fully tested. These cracks are so small that they are only discernible by the most modern techniques of ultra-sonic testing. They represent an additional maintenance task, but they do not involve the crews of the boats in any degree of risk.
§ Mr. Iremonger
asked the Secretary of State for Defence if he will make a statement on the British nuclear submarine programme.
§ Mr. J. P. W. Mallalieu
The precise rate at which we shall go on building nuclear-powered fleet submarines has not yet been settled, but we plan to order a sixth boat early in the New Year.