Perhaps I had better start this paper by denning exactly what is meant by ultra high tensile steel. During the Second World War and for some years afterwards, 80 to 90 tsi (i.e. 180 to 200 ksi) ultimate tensile strength was considered to be the highest safe range at which structural steel could be used, due to the lack of sufficient toughness or ductility at higher strength levels. This lack of toughness and ductility is particularly important in applications such as landing gears, in the design of which it is often impossible to avoid conditions where the principal stresses are perpendicular to the grain direction: in such applications, adequate transverse toughness and ductility are vital necessities. In more recent years, steels of higher strength, combined with adequate toughness have been developed, and thus the term “uhts” has become to mean those structural steels capable of attaining a tensile strength of over 90 tsi (200 ksi), combined with adequate toughness. In practice, the current state-of-the-art is that landing gears are now being regularly manufactured in steel in the 122–134 tsi (275–300 ksi) range, while designers are asking for steels of still higher strength combined with adequate toughness (up to 220 tsi, 500 ksi), and claim that the gross weight of the aircraft could be substantially reduced if and when such materials become available. It is interesting to note, however, that although the strength of uhts has in general increased from 90 tsi in 1947 to 130 tsi (300 ksi) in 1970, there is no evidence of the future availability of stronger steels than this latter figure, i.e. it looks as though we are stuck with this strength level as a maximum for future applications.