A gas turbine engine assembly including an improved apparatus for cooling the combustor (12) to preclude thermal failure of the combustor (12) and to preclude NOx formation. The system includes a liquid pump (40) driven by the turbine shaft (16) and supplying a cooling fluid to an annular cooling chamber (24) defined around the central combustion chamber (22) of the combustor. The cooling fluid is thereby placed in heat exchange relation to the combustor (12) to absorb heat from the combustion products within the combustion chamber and convert the fluid to a relatively higher energy condition, whereafter the fluid in its high energy condition is injected into the combustion chamber (12) for mixture with the combustion products and delivery with the combustion products to the turbine inlet. The cooling liquid may totally fill the annular cooling chamber around the combustion chamber (12) or may partially fill the annular cooling chamber (24), or the cooling fluid arriving at the annular cooling chamber (24) may already be in a gaseous state so that the cooling chamber is totally filled with a vapor (46).