The first L-23As entered service in 1953 and the type served the US Army for almost forty years, the last U-8Fs being retired in 1992. When US military aircraft designations
were revised in 1962, the remaining L-23D, RL-23D, L-23E and L-23F aircraft became
U-8Ds,
RU-8Ds,
U-8Es and
U-8Fs. A further 47 Model 65s were ordered in 1962 and 1963 as U-8Fs; one of these was delivered to the
Pakistan Army, formally the only L-23 or U-8 delivery to a foreign user (although other nations bought Queen Airs
off-the-shelf as military aircraft). These were the final new-build aircraft in the series, however the unique Beechcraft Model 87
turboprop proof-of-concept aircraft used in developing the
King Air was delivered to the Army as the
NU-8F in 1964 (this was later re-designated the
YU-21) and a few used Queen Airs were also taken by the Army. Many U-8Fs were modified during their service lives to a similar standard as civilian Excalibur Queen Airs. The most obvious modifications are more powerful
Lycoming IO-720 eight-cylinder engines in place of the factory-fitted six-cylinder engines; and bulged main landing gear doors that fully enclose the wheels when the gear is retracted instead of the wheels partially protruding through the doors. Many L-23Ds/U-8Ds and U-8Fs have been registered as civilian aircraft since retirement from military service. ==Variants==