Derco is working with Hamilton Sundstrand to develop and market environmental control system upgrades for all models of F-5 and T-38 fighter and trainer jets. Milwaukee-based Derco will invest in related engineering and development work associated with the new upgrades. The company already is marketing an enhanced version of the F-5F ECS. Hamilton Sundstrand is the original manufacturer of the F-5/T-38 Refrigeration Pack. The upgrade helps meet the increased cooling needs of modern avionics.