In the years 1972-1976, PRIOR to the Delta/Western merger, Delta flew all three of the then available widebodies (747, L-1011, DC-10). They had ordered the L-1011 but due to production delays, they also took delivery of the DC-10. They also were flying the Fairchild F-27, Douglas DC-8, Douglas DC-9, and Boeing 727....and making nice profits.. that's what SEVEN fleets? I guess they hadn't heard of the "three fleet rule" lol
The L-1011 was in Delta service from about 1973 to 1992, the DC-10 from about 1972 to 1987, and the 747 from 1970 to 1977.
The MD-11 was also in the Delta fleet from 1990 to 1996 so for a couple of years (1990-1992), Delta was flying two types of widebody trijets at the same time.
After National merged into Pan Am, Pan Am also flew the DC-10 and L-1011 together, along with the 747.