The Daimler L21 or Daimler-Klemm L21 was a light twin engined, single seat, parasol winged sports aircraft built in Germany.
Haplogroup R1b (R-M343), also known as Hg1 and Eu18, is a human Y-chromosome haplogroup.
HMS L21 was a L-class submarine built for the Royal Navy during World War I. The boat was not completed before the end of the war and was sold for scrap in 1939.
The Piper PA-18 Super Cub is a two-seat, single-engine monoplane.
This family is a putative ribosomal protein leader autoregulatory structure found in B. subtilis and other low-GC Gram-positive bacteria.
USA-193, also known as NRO launch 21 (NROL-21 or simply L-21), was a U.S. military reconnaissance satellite (radar imaging) launched on 14 December 2006.