The second of three S-2s registered as N426DF. Delivered to the US Navy as S2F-1 136613. Redesignated as an S-2A in 1962. Stored at Davis-Monthan AFB, AZ in 1978. To the California Department of Forestry as N426DF in 1985. Converted to a Tutbo Tracker by Marsh Aviation and first flew as such in 1986. To Marsh Aviastion as N613MA in 1999 and stripped for parts at Mesa-Falcon Field, AZ. Still there in 2023.

Registration N426DF was later re-used on Turbo Tracker c/n 293C.

Marsh Turbo Tracker demonstration aircraft, with additional "Marsh Propulsion Applications" titles on the nose. Registration N426DF was used on three Trackers: from 1974 to 1985 on c/n 216 (which was never taken in service), from 1985 to 2000 on this aircraft c/n 522, and as of August 2000 on c/n 293C.