I dunno who came first, but the DT was a 1968 iteration and there are 300 series and 400 series engines. Of the 300's, there were DT312,DT360, and DT361's. The 400 series had the DT407,DT408,DT414,DT436,DT466. The DT466 was used in IH trucks from 1975 on. Login to read more.