increase that became a regular feature of the engine's improvements in its subsequent versions: the PC2.3 in 1971, PC2.5 in 1973 and the 550 kW per cylinder PC2.6 in 1981. A dual-fuel version (gas and diesel) was also developed, while the range had its final addition in 1995 with the PC2.6B long-stroke engine. This final version featured a cast-iron engine mounting, a simpler design and a power output of 750 kW per cylinder – four times the power of the original model from 1953. In 1969, the PC3 engine was launched. It had a 480 mm bore with a power output of 700 kW per cylinder. In 1972, SEMT introduced the PC4 engine. It had a 570 mm bore and produced 990 kW per cylinder. With the PC4.2 version in 1981, it increased to 1,215 kW per cylinder. The PC4.2 B long-stroke model in 1985 raised the output to 1,325 kW per cylinder. In its 18-cylinder version, the latter model was one of the most powerful four-stroke engines on the market in its time. PA engine line The PA engines were high-speed units, running at more than 1,000 rpm. The initial PA1 and PA2 models could be seen as miniature versions of the PC engines, with a bore of 175 mm, and could be used for a wide range of applications – including powering submarines. The first turbo-charged version of the PA developed 46 kW per cylinder at 1,250 rpm. Launched at the end of the 1950s and initially developing 110 kW per cylinder at 1,500 rpm, the PA4, with an initial 185 mm bore, was a completely new design. It would later be developed with a VG version (variable geometry combustion chamber) and subsequently with a 200 mm bore to increase the power. A dual-fuel version (diesel fuel and gas) would also be developed. In 1978, the PA4 VGDS was launched. It had a twin-stage turbocharger to power naval ships, generating 184 kW per cylinder. The final model in the range was launched in 1988. This was the PA4 200 VGA for rail and naval applications, producing 165 kW per cylinder with a single-stage turbo. Specific versions for submarines were also developed: the PA4 185 SM, PA4 200 SM, and PA4 200 SMDS with twin turbo-charging. PA6 engine line In 1966, planning started for the PA6. It was designed to be the most powerful engine that could be fitted