There were about 1000 German U-boats built over the course of World War 2.
The main German sub was the Type 7C which was about 800 tons and 67 meters (220 feet) long.
Currently the USA has about 55 nuclear submarines that cost about $1-3 billion each. On average the cost of each submarine is about $1.6 to 2 billion. The annual operating cost for any of these subs is approximately $21 million. The typical service life of a nuclear sub is about 30 years. Refueling and modernizing at the half-life point costs about $200 million. Near the end of the service life, another refueling and extensive overhaul for about $410 million will extend the life another 12 years, for a total service life of 42 years. This totals to about $3.6 billion in constant dollars over the lifetime of a Seawolf class sub.
Air independent diesel electric can cost about $100 to 300 million. Operating costs are lower. Automation can reduce the crew required and further reduce costs. Mass production of robot submarines could see unit costs at $50 million.
Roughly $100 million for the Swedish Gotland submarine
Current DARPA is a robotic surface ship but robotic submarines will likely be developed
James Fanell (x- Navy captain and naval expert), prediced China's Navy would grow to include 99 submarines of all types, four aircraft carriers, 102 destroyers and frigates, 26 corvettes, 73 amphibious ships and 111 missile craft. All told, Fanell predicted, the Chinese Navy of 2030 will comprise 415 ships. This is up from about 300 ships now. This is based upon a projection of the current rate of production for the Chinese Navy. China building about 10 new submarines each year.
If there were an escalation of the submarine arms race that is currently beginning and the shift to low cost Air independent diesel submarines continued, then the 55 expensive US nuclear submarines could eventually be replaced by 1000 to 2000 robotic submarines and AIP diesel submarines. The USA and China could afford to spend $5 to 15 billion per year building up to the 1000 to 2000 low cost and robotic submarine fleet levels over ten years.
'Picking up the quiet hum of a battery-powered, diesel-electric submarine in busy coastal waters is 'like trying to identify the sound of a single car engine in the din of a major city,' says Rear Admiral Frank Drennan, commander of the Naval Mine and Anti-Submarine Warfare Command.
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