A gas turbine engine has been proposed that uses a near constant temperature (NCT) cycle and Inter-Turbine Burner (ITB) to provide large amounts of power extraction from the low-pressure turbine. This level of energy is achieved with a modest temperature rise across the ITB. The additional energy can be used to power a large fan for an ultra-high bypass ratio transport aircraft, or to drive an alternator for large amounts of electrical power extraction. Conventional gas turbine engines cannot drive ultra-large diameter fans without the use of excessive turbine temperatures, and cannot meet high power extraction demands without a loss of engine thrust. Reducing the size of the main combustor and ITB is essential to reducing or maintaining overall engine weight and size for the NCT cycle. Concepts for an ultra-compact combustor (UCC) are being explored experimentally. The basic combustor design involves flame-holding in a cavity within which the flow is strongly swirled. Experimental results at atmospheric pressure indicate that the combustion system flame holding zone operated at 95 - 99 percent combustion efficiency over a wide range of operating conditions. Flame lengths were extremely short, at about 50 percent those of conventional systems.