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Current diesel-electric trains are designed to draw their power from overhead lines on electrified sections of track.

Where diesel-electric submarines spend half of their time at sea going to from a patrol area, a nuclear-powered submarine would spend 15-20% of its time in transit, he said.

Huang said Taiwan's diesel-electric submarines can keep China at bay within the first island chain, referring to the area that runs from Japan through Taiwan, the Philippines and on to Borneo, enclosing China's coastal seas.

Next to it, one of Russia's Kilo class diesel-electric submarines, the Rostov-on-Don - used to launch Kalibr cruise missiles hundreds of miles into Ukraine - had "likely suffered catastrophic damage".

The submarine shown in state media reports on Friday appears to be a reworked diesel-electric powered Romeo-class Russian submarine — a model dating back to the 1950s.