R-755A1 The base-line direct drive production version.[2] R-755A2 300 hp variant. R-755B1 De-rated version of the R-755A to drive a fixed pitch airscrew.[2] R-755B2 De-rated version of the R-755A to drive a variable or controllable pitch airscrew.[2] R-755E Up-rated engine with reduction gearing.[2] R-755EH Developed to power the Jacobs Type 104 Gyrodyne.[2]