It was designed and built by the Kreider-Reisner Aircraft Company of Hagerstown, Maryland.

Puckett states "over 200 were built in 6 different models.

"[4] The KR-21-A was a wire braced biplane with two open tandem cockpits and powered by a 100 hp (60 kW) Kinner K-5 radial piston engine.

[2] It was of mixed construction and had a fixed tailwheel landing gear and was fitted with dual controls.

[2] The KR-21-B was a more powerful biplane development, using a 125 bhp Kinner B-5 engine.