Realised that most modern submarines (and some aircraft carriers) use nuclear power, but destroyers and frigates don’t. I don’t imagine it’s a size thing, so I’m not sure what else it could be.
In: Engineering
Sharks vs dolphins is why military subs often use nuclear.
Sharks have gills so don’t need to surface, ever. You don’t know they’re there unless you’re in danger.
Dolphins can stay under water for a really long time, but they need to breathe air.
Nuclear power doesn’t need oxygen. Diesel does (augmented by battery and liquid oxygen, but that runs out way faster than nuclear fuel).
Nuclear is generally too expensive and politically unpopular for ships that don’t live in an oxygen-free environment.
Really short ELI5 version: It’s in a submarine because it lets a submarine pursue and destroy targets while remaining submerged, in a way no other plant can. It’s in almost nothing else because it’s expensive – but it used to be in other things!
Longer version:
Nuclear reactors in a naval vessel offer three big advantages: air independence, unlimited range, and horsepower.
For a submarine to stay submerged, it needs to be air independent for at least a period. For long patrols, it needs to carry enough fuel. Other systems have this as well, so what make the difference compared to other air independent propulsion is the amount of power available. Moving underwater requires much more energy than moving a ship on the surface, so **without a nuclear reactor a submarine, when submerged, becomes a smart naval mine**. It can maneuver around some, even into the teens of knots, but warships on the surface move at more than twice the speed when in a combat area, with the fleet speed of Halsey’s fleet during WWII over 25 knots. With the available horsepower, a submarine is now capable of pursuing and destroying targets, instead of waiting and being lucky. It becomes an, “Attack,” submarine. To put it in perspective how much is available, the battleship USS New Jersey (BB-62) displaced 45,000 tons and had 212,000 horsepower, and hit almost 34 knots in 1968; the submarine USS New Jersey (SSN-796) displaces 17% of that, and has 260,000 horsepower. And for how important speed is, during WWII most US submarines attacked on the surface rather than submerge, so they could keep their speed up.
For an aircraft carrier, it needs to get wind over the flight deck in order to conduct flight operations, so it has to be fast, which means more horsepower, big engines, and a lot of fuel. And just the air wing itself has a voracious fuel appetite, so by using a compact nuclear reactor, you’re able to achieve the same or higher speeds while giving more room to armor and consumables.
For other ships, there were nuclear powered cruisers and destroyers that were decommissioned at the end of the Cold War. They were sent around the world with the first nuclear powered aircraft carrier in Operation Sea Orbit in 1964, but were not significantly developed further because despite the advantages, they were very expensive to run, and nuclear reactors can only be so small due to the shielding, so they were replaced by gas turbines in modern destroyers and cruisers as they take up less room in the ship, even with fuel, and were cheaper and easier to run.
If you want to learn more about why nuclear propulsion matters for submarines, anything by Bill Toti discussing submarines (he’s been on several podcasts) is a goldmine. Also what it’s like to not have a nuclear plant, Thunder Below by Eugene Fluckey.
That’s a good question that doesn’t have an obvious answer.
The largest container ships cost hundreds of millions to produce (plural) and operating costs exceed $100k per day. They also burn bunker fuel which is dirtier than diesel. All told, emissions from the global fleet of more than 5,000 container shipping rival that of the estimated 1.5 billion gasoline cars in operation on earth, combined.
A zero-carbon future would almost certainly have to include most of the larger commercial shipping vessels transitioning to nuclear power.
two main reasons it’s more common than on surface ships (the us has a number of nuclear powered aircraft carriers and there are a handful of other nuclear powered ships out there)
you can’t fuel a submarine with a combustion power source unless it is surfaced or snorkeling. this makes them much easier to detect, and staying undetected is the main reason submarines exist. a conventional submarine has to use batteries while fully submerged, which last a much shorter time between being able to be detected. as such an enemy can always be at least aware in what region a submarine is since the range without surfacing is limited.
the second reason is just performance. a nuclear powered submarine is much faster while underwater because it has massive power reserves and it can also use that power for more advanced sensors like powerful sonar and things like powerful lasers and underwater oxygen generation through electrolysis.
overall a nuclear submarine is just much faster while submerged, can take on much longer distance and duration missions, can do so fully submerged to keep undetected and can have more energy intensive equipment on board
Essentially, the only limiting factor for a Nuclear sub, is Weapons (Torpedoes) and food for crew. That is it, the reactor can go for YEARS.
They make their own air, and water, compared to WWII submarines that while they remained underwater, they could only run on Batteries, because of Diesel engines.
It was a Nuclear Submarine that sank the Argentine General Belgrano, Britain’s HMS Conqueror, and was then the FIRST Nuclear submarine to have fired its weapons in an active conflict (Fired in Anger). It took 20 minutes for the ship to sink from the 2 torpedoes that hit (Out of 3 fired), Second of which hit the bow, Severing it clean off of the ship.
Conqueror’s Jolly Rodger, in a museum. https://www.wearethemighty.com/wp-content/uploads/legacy/assets.rbl.ms/17310585/origin.jpg?strip=all&quality=95
Quite a few surface military vessels do.
https://en.wikipedia.org/wiki/Nuclear-powered_cruisers_of_the_United_States_Navy
https://en.wikipedia.org/wiki/Nimitz-class_aircraft_carrier
This is the funny thing though. They use the nuclear energy to heat water to use the steam to power everything. It’s basically a high tech steamboat
The biggest issue is that nuclear power is fairly expensive. While you no longer need to bring in fuel, it takes a lot of engineering to built a reactor and highly trained operators to keep it running safely. The [nuclear training program](https://en.wikipedia.org/wiki/Nuclear_Power_School#Nuclear_Power_Training_Unit) is one of the more grueling the US Navy offers, and each nuclear ship requires multiple officers per shift as well as a number of enlisted per shift.
Submarines drastically benefit from nuclear as its *extremely* quiet and thus extremely hard to detect. It can also be operated while fully underwater for extended periods, which no other (current) power source can manage. This makes nuclear a massive benefit for submarines.
Carriers, being as massive and critical as they are, also benefit from the near constant operating ability, and the extra training required for operation is minor compared to all the other staffing costs. Carriers still need to carry a ton of fuel for the planes they are flying, so not having to *also* carry the fuel for the ship itself ensure the ship has enough space for other needs. These ships also need a ton of power for both propulsion and aircraft launch catapults, with other systems often requiring significant amounts as well as the carriers are typically the main command hub of a navy.
On smaller surface ships, its just not worth the costs. The US did operate a number of [nuclear cruisers](https://en.wikipedia.org/wiki/Nuclear-powered_cruisers_of_the_United_States_Navy) from 1961 until 1998. There are, however, still a couple of [nuclear icebreakers](https://en.wikipedia.org/wiki/Nuclear-powered_icebreaker#List_of_nuclear-powered_icebreakers) in operation, which are basically a civilian cruiser – all such ships are currently operated by Russia.
Cost/benefit analysis.
Submarines and Aircraft carriers are few in number so the cost is worth it. Submarines need to be able to go as long as possible without surfacing for refueling/resupply so nuclear is best. Aircraft carriers are so massive that a nuclear reactor makes the most sense. Everything else it makes more sense to just use conventional fuels.
Well, there are 2 other options: diesel fuel, or batteries.
How exactly do you expect a submarine to burn diesel, at depth, for days, weeks, or months on end?
Similarly, batteries are able to last at most, a few hours. Certainly not days or months.
So, that leaves, nuclear power.
Latest Answers