# Would nuclear fusion ever be practical for marine propulsion? **URL:** \ **Category:** Factual Questions\ **Created:** [June 27, 2026, 7:22pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233 "2026-06-27T19:22:03Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![spacecadet86](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@spacecadet86](https://boards.straightdope.com/u/spacecadet86)\ **Post date:** [June 27, 2026, 7:22pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/1 "2026-06-27T19:22:03Z")
The navy has plenty of nuclear carriers and submarines operating by splitting atoms instead of combining them. If ever fusion reactors on land start generating a great deal more energy than is put into them to get fusion started, could the technology by scaled down to fit inside ship hulls or submarine hulls and provide nuclear fusion marine propulsion to replace fission? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [June 27, 2026, 7:29pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/2 "2026-06-27T19:29:07Z")
Nobody knows. Because we don’t have a functioning fusion reactor yet. One could make educated guesses based on how scalable current designs are. But since zero of those current designs are anywhere close to working, you’d be extrapolating from near zero data. Come back and ask again after we have working fusion reactors. ---
**Author:** ![Dahu](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dahu/32/3416_2.png) [@Dahu](https://boards.straightdope.com/u/Dahu)\ **Post date:** [June 27, 2026, 10:48pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/3 "2026-06-27T22:48:24Z")
How long will that be? ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [June 27, 2026, 11:00pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/4 "2026-06-27T23:00:03Z")
Its been 10 more years down the road for something like over 50 years now. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [June 27, 2026, 11:10pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/5 "2026-06-27T23:10:14Z")
We may as well ask which sort of **[Galleon -Wikipedia](https://en.wikipedia.org/wiki/Galleon)** is the best aircraft. ---
**Author:** ![dcbwhaley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcbwhaley/32/21437_2.png) [@dcbwhaley](https://boards.straightdope.com/u/dcbwhaley)\ **Post date:** [June 28, 2026, 9:30am UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/6 "2026-06-28T09:30:37Z")
A working fusion reactor is ten years away. Has been for half a century Rather like Unix replacing Windows ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [June 28, 2026, 10:23am UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/7 "2026-06-28T10:23:22Z")
Ten years is an underestimate. Usually it has been thirty years in the future. Always has been, always will be. A few of the fusion startups are claiming reactor designs that are very small. Easily ship fit size. Of course they don’t actually work. But some seem to have burnt though a quite a lot of investors money. Not quite fusion, but someone is being kept warm and happy. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [June 28, 2026, 11:32am UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/8 "2026-06-28T11:32:02Z")
The technologies that might plausibly give us a continuously-operating, energy positive reactor will likely be too big, heavy and complex. But of course, as it’s still WIP, no-one knows for sure. As a slight aside / hijack, the temperatures and pressures required to get nuclei to fuse is a good illustration IMO of how much stronger the other physical forces are to gravity. Even the sun’s tremendous mass, resulting in incredible pressures on the smallest nuclei possible…can’t quite get them to fuse. It needs quantum tunneling to get over the remaining energy hump. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [June 28, 2026, 12:40pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/9 "2026-06-28T12:40:59Z")
Any heat source can be made into a naval propulsion source. The question is purely whether it will ever be possible to have a small enough fusion plant to put on a ship. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 28, 2026, 3:56pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/10 "2026-06-28T15:56:12Z")
Some ships are pretty big, though. Even without knowing how large a hypothetical fusion plant would be, it’s hard to imagine it being too big to fit on an aircraft carrier. > [@dcbwhaley](#): > > Rather like Unix replacing Windows Completely? That’ll probably never happen. But I’m pretty sure that the number of Unix devices in use passed up Windows years ago. Consider that MacOS, IOS, Android, and ChromeOS are all Unix. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [June 28, 2026, 4:07pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/11 "2026-06-28T16:07:23Z")
> [@Chronos](#): > > Some ships are pretty big, though. Even without knowing how large a hypothetical fusion plant would be, it’s hard to imagine it being too big to fit on an aircraft carrier. Well, a friend in the Princeton physics department once said he believes the only practical way to contain nuclear fusion is with gravity. That reactor won’t fit on any ship. 😉 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 28, 2026, 4:23pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/12 "2026-06-28T16:23:17Z")
It won’t fit on an onshore power plant, either, though. And if you’re talking about the power plant just using collectors for the power, that was the primary propulsion source for ships for millennia: They just figured out a way to use the planet’s entire atmosphere as their collector. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [June 28, 2026, 4:32pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/13 "2026-06-28T16:32:45Z")
Yes, there’s a real chance that we will never have a practical on-shore fusion power plant. That was my point. And obviously, we use lots of fusion power indirectly: through burning wood, coal, etc., via wind, via dams, and via solar panels. Probably someone else I’m missing, too. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [June 28, 2026, 7:38pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/14 "2026-06-28T19:38:56Z")
In a way, fission power is also (indirectly) stellar fusion, because uranium and plutonium, like all elements heavier than helium, were forged within stars of the distant past via stellar nucleosynthesis. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [June 28, 2026, 7:54pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/15 "2026-06-28T19:54:24Z")
Very explodey stars, perhaps. ---
**Author:** ![EdwardFound](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@EdwardFound](https://boards.straightdope.com/u/EdwardFound)\ **Post date:** [June 29, 2026, 5:49pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/16 "2026-06-29T17:49:27Z")
Say we get to the point of building reactors by assembling clouds of hydrogen gas massive enough to sustain fusion by gravitational pressure: Would it be possible to keep the reactors running continuously by drawing off helium while feeding in more hydrogen - or would we just need to decommission them when they reach end-of-life? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 29, 2026, 6:16pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/17 "2026-06-29T18:16:35Z")
I think that by the time you get to “what if we made our own stars”, you’re well beyond the point at which any sort of technological extrapolation is remotely valid. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [June 29, 2026, 6:38pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/18 "2026-06-29T18:38:14Z")
I approve this post! ---
**Author:** ![solost](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/solost/32/11776_2.png) [@solost](https://boards.straightdope.com/u/solost)\ **Post date:** [June 29, 2026, 7:02pm UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/19 "2026-06-29T19:02:37Z")
> [@LSLGuy](#): > > We may as well ask which sort of **[Galleon -Wikipedia](https://en.wikipedia.org/wiki/Galleon)** is the best aircraft. That’s easy-- the Flying Dutchman, of course. ---
**Author:** ![Ancient\_Nerd](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ancient\_Nerd](https://boards.straightdope.com/u/Ancient_Nerd)\ **Post date:** [June 30, 2026, 6:56am UTC](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233/20 "2026-06-30T06:56:33Z")
> [@EdwardFound](#): > > clouds of hydrogen gas massive enough to sustain fusion by gravitational pressure That would be a star. [Next page](https://boards.straightdope.com/t/would-nuclear-fusion-ever-be-practical-for-marine-propulsion/1031233.md?page=2)