potential disadvantage of this embodiment is that a thermal imbalance is created between the temperatures of the cathode air and the fuel gas entering the second sub stack which can create undesirable mechanical stresses therein alternatively other gasses could supplement or replace second stream 412 in this injection scheme most notably stream 412 could be augmented with oxygen this would be especially useful if multiple more than 2 substacks were series flow connected in a substack module such gas tailoring or selection could impact the sofc chemistry in downstream substacks as well as provide additional cooling as already noted referring to fig6 a fuel cell stack module 500 in accordance with the invention comprises a first sub stack 511 a a second sub stack 511 b a precooler heat exchanger 540 ahead of the first sub stack and an intercooler heat exchanger 530 between the sub stacks which arrangement is substantially as described above in addition module 500 includes a temperature sensor t 2 in the gas flowstream between precooler 540 and first sub stack 511 a to monitor the temperature of the cathode air 512 entering the sub stack which may be equal to the temperature of fuel gas 520 if their respective temperatures have been previously equalized to a temperature t 1 during passage of the gases through opposite sides of an equalizer heat exchanger 502 outside module 500 a first coolant 580 may be passed through precooler 540 to adjust entry temperature t 2 as desired a temperature sensor t 3 monitors the temperature of the gas exhausts from first sub stack 511 a and a temperature sensor t 4 monitors the entry temperature of gases into.