In late 1964, Saunders-Roe commenced design work on multiple hovercraft designs; in addition to the relatively huge SR.N4 and studies into a prospective 2,000 ton freighter, there was also interest in developing its existing smaller hovercraft range [REF].
The first craft to be lengthened in this manner, in effect becoming the first SR.N6, was the ninth SR.N5 to have been produced [REF].