The Spanish navy has begun construction of four S-80 "Scorpene" class subs, at a cost of some $280 million each. These are of Spanish design and feature air-independent engines. Modern air-independent engines for submarines began to appear in the late 1980s, when Sweden installed Stirling type power plants in their Nacken class subs. The S-80s will be 235 feet long, displace 2,100 tons on the surface, have a crew of 40 and be highly automated. The design also concentrates on quietness and a powerful American built electronic sensor and fire control system. The six 21 inch torpedo tubes will also be used for mines and cruise missiles. Some of the construction will take place in France.