The Mi-26 Halo is a twin-turbine heavy-lift helicopter. It is the world's largest production helicopter. The Halo's development started in the early 1970s. The designer's goal was to produce a helicopter with a load capacity twice that of any contemporary helicopter. The first Mi-26 Halo prototype flew in December 1977 and was first displayed at the Paris Air Show in 1981. In 1982, Russian squadrons received their first Halos, which were not fully operational until 1983. In 1986, India was the first country to purchase a Halo. Since then Halos have been sold to nearly twenty countries. The cost of a Halo is between $10 million and $12 million.