As the thread has drifted into Military Linguistics rather than Aviation. I shall admit that, like Airsound, I once understood the ablative absolute and the jussive subjunctive but they are now obscured by time. However, ferendo is a masculine singular gerundive, in either the dative or ablative case; so a better translation might be
I strike (by) being carried. Mind you some of Transport Command's former customers may have preferred the alternative meaning of ferendo -
to be endured. Maybe one was responsible for the bad translation!
I am sure the intention was to reflect Transport Command's contribution to the frontline by getting ordnance and personnel where they were required to be ready to fight. I believe the United Kingdom Mobile Air Movements Squadron preferred the translation "We fight by carrying".
To answer Eckhard more fully "ferry" is derived from the Old Norse
ferja meaning ferry boat and hence like (2)16Squadron pinched from nautical origins.
?