plane ▁built ▁in ▁the ▁United ▁States ▁in ▁the ▁late ▁ 1 9 2 0 s . ▁It ▁was ▁developed ▁by ▁Gro ver ▁Lo ening ▁from ▁the ▁C - 1 ▁that ▁he ▁had ▁created ▁together ▁with ▁L ero y ▁Gr um man , ▁incorpor ating ▁a ▁new ▁fus el age ▁design . ▁This ▁depart ed ▁from ▁the ▁characteristic ▁Lo ening ▁design ▁feature ▁of ▁having ▁a ▁sl ender , ▁" sh oe horn " ▁float ▁project ing ▁from ▁the ▁unders ide ▁of ▁the ▁fus el age ▁with ▁an ▁engine ▁mounted ▁tra ctor - f ashion ▁above ▁it . ▁Instead , ▁the ▁C - 4 C ▁had ▁a ▁conventional ▁flying - bo at ▁h ull , ▁with ▁an ▁en closed ▁cabin ▁for ▁passengers . ▁The ▁engine ▁was ▁mounted ▁in ▁a ▁separate ▁nac elle ▁on ▁the ▁leading ▁edge ▁of ▁the ▁upper ▁wing . ▁ ▁Two ▁C - 4 C s ▁were ▁built ▁in ▁ 1 9 2 8 , ▁shortly ▁before ▁the ▁corpor ate ▁mer ger . ▁In ▁ 1 9 3 1 , ▁Ke yst one - Lo ening ▁built ▁two ▁examples ▁of ▁a ▁re vised ▁version , ▁but ▁no ▁further ▁production ▁en su ed . ▁ ▁Thompson ▁Aer onaut ical ▁Corporation ▁( TAC ), ▁a ▁U . S .- based ▁air ▁car rier , ▁was ▁operating ▁scheduled ▁passenger ▁service ▁between ▁Detroit ▁and ▁Cleveland ▁in ▁ 1 9 3 0 ▁with ▁Ke yst one – Lo ening ▁Air ▁Y acht ▁aircraft ▁with ▁six ▁round ▁trip ▁fl ights ▁a ▁day ▁between ▁the ▁two ▁cities . ▁ ▁Spec