Mr. Eickhoff appears to have misunderstood the very nature of the project, which is not to develop a steam locomotive to compete with diesel and electric traction in normal commercial service - an aim which would be quite Quixotic for railways in economically developed countries. The quest for something "revolutionary" does not therefore apply. The limited resources ever likely to be made available for a new steam locomotive would preclude this kind of development, nor would they allow an extended period of practical work "to sort out the problems", which would be horrendously expensive - and it must be added that the controller of the railway infrastructure would be highly unlikely to allow its track to be used for such experimental work. In fact exactly the opposite must be aimed for, i.e. excellent reliability more or less from the word go. This rules out "revolutionary" developments, which very seldom work first time. There is an engineering maxim that after a prototype a second machine has to be built to get it right, and as this is a luxury we are unlikely to have the 5AT must be what we know will work. And that is all it needs to be, for it is not a "radical solution" (what radical solution? we may ask) but sound engineering in the Porta manner which is able to transform performance to an altogether higher level than hitherto known, without changing the steam locomotive's classical simplicity.

The question of Walschaerts versus Caprotti valve gear has been partly dealt with in the reply to Mr. Attewell. To answer Mr. Eickhoff's points, the contribution of Walschaerts valve gear to the balancing issue is negligible as most of its inertia forces are out of phase with those of the main reciprocating masses, and the maximum acceleration (i.e. inertia force per unit mass) of even ultra long travel valves is only some 30% of that of the pistons.

Although altering the valve events by changing the cams may be convenient on an "experimental machine", the terms of the project mean that the design of the 5AT is in no way intended to be experimental.

Chapelon's reservations about piston valves are no longer valid. Porta's invention of valve liner cooling allows higher steam temperatures to be used without lubrication difficulties, and inertia forces are kept at manageable levels by the very lightweight construction made possible by designing the valves according to stress analysis rather than empirical rules. It is also worth noting that Chapelon's final masterpiece, the 242A-1, as well as his aborted 152P design, had piston valves driven by Walschaerts gear. No recourse to poppet valves needs to be considered before the possibilities of piston valves have been fully explored - which is what the 5AT will do.

Compound expansion for the 5AT has been considered - and rejected. The arguments for and against compounding are too complex to air here, but I am firmly convinced that for a high-speed locomotive such as the 5AT simple expansion - using all the cylinder refinements that are now possible, but which are not common knowledge - is the right choice. Mr. Eickhoff states that the compound has left the simple to catch up - well, I believe the 5AT will show that it has now fully caught up, and indeed probably surpassed the compound for power generation at high speed.

Finally, just to correct any misconception that might have arisen from the final paragraph of the News article on the 5AT project (S.R. No. 273, page 14), it is the fundamental design calculations, not the engineering drawings, which are being worked on.