As can be imagined, there were considerable variations in a design which spanned 15 years, and modifications as a result of war experience could only be incorporated depending on the stage of construction reached. Although not, in themselves, above average, the combination of the S boats' qualities, together with the reliability of their equipment and the great ease of operation and maintenance, made them very effective and safe.
No modifications were made to the first five vessels of the War Programme (Safari, Sahib, Saracen, Satyr and Sceptre), but an external stern torpedo tube was added to the group of boats that followed, bringing the number of tubes up to seven, and the number of available torpedoes to 13. This change was indicative of the varied armament of S Class submarines. Many boats were
