The introduction of a gas turbine having a split compressor (instead of a split turbine) with the two compressor parts and the power transmitting shaft linked by a differential gear seems to be a further important step in realizing a specific gas turbine for propelling vehicles. The fact that the turbine is undivided allows a free choice of the most suitable design of this component. The choice of the gear ratio permits adjustability of gas turbine performance to any particular application. The inclusion of a suitable air preheater in the design of such a gas turbine is imperative and big strides have been made to realize such a heat exchanger. The introduction of non-metallic materials such as ceramics and the adoption of multi-drum design may decrease the parasitic weight, facilitate the ingress and egress of the two heat exchanging gases and at the same time eliminate any destructive effect of excess temperatures. The possibility of reducing costs by mass production makes the recuperative plate type heat exchanger an attractive proposition. Mass production is facilitated if the whole heat exchanger is subdivided into a number of similar self-contained elements. It is useful to keep these elements small so as to limit distortion caused by thermal expansion, to reduce the parasitic weight ratio to an acceptable figure and to allow the adjustment of a heat exchanger to the needs of different types of gas turbine units. It is also possible to exchange these elements easily and to reduce maintenance costs. Standardization of these elements will be possible allowing of their universal use for different designs and sizes of gas turbine units. This will relieve firms engaged in developing and producing such units for vehicle propulsion from including the air preheater in the programme. New protective methods such as ceramic coatings for parts of the elements which are directly exposed to the hot gases will improve reliability and serviceable life of the heat exchanger.