I've always found the idea of intelligent every-man sent back in time using his knowledge of the future tech to realistically impact the past. The first time something like this came to my mind was in computer science class when it finally struck me just how drastically our computer hardware has increased, and how impressive it would be to go back to the beginning of the computer age with my laptop and knowledge of all our programming history to shape it.

One of the obvious things to do with a story like this would be to drop someone into the World War II and Cold War eras. Let's say I suddenly showed up right at the beginning of World War II, and somehow managed to show my laptop to someone important enough to get funded to support the war effort. First, how hard would it be to write a program to brute force break Enigma, or similar a scheme they may switch to once they realize Enigma was broken?

I know how to brute force break a simple cypher, but I don't know Enigma's approach as well. As I understand there were 3-4 dials they could switch from, so if I simply iterated through every option for each 'dial' till I get a valid looking message would that be sufficient, or was Enigma more complex then that? I would need to get a Japanese and German dictionary in my computer, if I don't have one already hiding out in Word somewhere presumably some typists would be required to trade off typing duties for a week to create the dictionary file.

Once an Enigma brute force approach was written what would happen? Let's assume that the presence of the laptop was kept secret from the enemies. Would the Allies abuse their cracking system excessively on the grounds that even if the Axis changes its encryption a new brute force solver could be hammered out within a week or so of scripting? Or would figuring out how something was encrypted to know how to brute force it be a sufficient enough challenge that we would still try to not reveal we had broken them?

What would it mean to the war effort to have Axis communication broken from day one? How significant a change to the war as a whole would occur?

For the sake of an interesting story, that doesn't make the time traveler a god, assume that the time traveler had not expected to travel in time and always hated history, and as such has a very limited knowledge that could be useful. Perhaps he knows a bit of Pearl Harbor, D-day, Midway, and the drop of Atomic Bombs, but nothing extensive and he is horrible with exact dates (no saying when Pearl Harbor happened, only that it did).

Finally, what other immediate or significant effects could such a travel have on the war? Assume a cheap laptop and basic (no more than newbie college graduate) programming skill, a general interest in the history of computer development and internet particularly, and a decent knowledge of science/physics and it's history as well. However, assume that the protagonist is not a hardware specialist and has only limited knowledge of computer architecture and hardware except for when it impacts software development and performance (no giving hints on how to build better computers faster).

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – user
    Commented Mar 19, 2015 at 20:50
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    $\begingroup$ Enigma was broken in WW2. However it was due to bad procedures involved in the messaging, not by raw computing power (although that helped). Brute-forcing Enigma is impossible even with modern laptops (possible using distributed computing and multiple machines though). Cracking the Enigma was kept a secret, especially from Germany. There's a lot more use in listening to your opponents, than making them talk less. $\endgroup$
    – Ordous
    Commented Mar 20, 2015 at 14:37
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    $\begingroup$ I really hope you brought your charger... $\endgroup$ Commented Mar 24, 2015 at 1:24
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    $\begingroup$ Our programming didn't really evolve that much. It is mostly the hardware that did. About 95% of ideas you could bring back aren't really that new - they were just unfeasible without something to run on. $\endgroup$ Commented Dec 21, 2015 at 17:20
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    $\begingroup$ Make sure you send them back with a copy of the documentation for their language of choice. I know I google MSDN and stackoverflow for a problem a lot, and I can only imagine the frustration of not being able to do that. $\endgroup$ Commented Jun 28, 2016 at 18:48

14 Answers 14


The biggest advantage I see being given here is simply processing power. You have a machine that can run calculations at a speed that would beggar imagination for someone living in that era.

In relation to the Artillery mentioned in another answer. Generally, an artillerist would consult his range tables to determine how to aim his cannon...rather than running all the math on the fly. You could easily generate more granular artillery tables to pass out.

The number crunching part of code breaking would be massively accelerated. Especially if you built an Enigma machine on the computer, gave it access to a German Dictionary (can be installed with many programs), and just told it to brute force code attempts until it started spitting out actual words.

Hell, give the physicists access to the Microsoft Calculator in Scientific mode, and they are likely to name their first born after you. Then write programs to run common mathematical formulas, and the Manhattan project would happen a whole lot faster. Seriously? Something that can calculate the cubic root of a 20 digit number, accurate to a dozen decimal places? In a matter of milliseconds!? GIMME!

All in all, the best thing he could do (sadly, this isn't very exciting) is to go to all the scientists and ask them for any number crunching that they need to do repeatedly...or any complicated calculations they needed to make, and either write programs to do it for them, or just run the numbers in MS Calculator.

Alternately, install a localized version of Candy Crush, lock out all other features of the computer, and give it to the Furher. Then, when he's so addicted to the game that he isn't paying attention anymore...you win! (kidding, of course)

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    $\begingroup$ plus one for the last paragraph ;) honestly I had imagined someone who is a quasi-pacifist as the traveler, someone fighting to get the computer to be used by scientist to increase quality of life for others, but also knows that the only way to do anything is get noticed, and that means code breaking. The whole moral aspect of being someone of both massive power (the laptop and his programing) and worthless (how to keep goverment from strong arming it away from you) while trying to do the right thing is the interesting part. $\endgroup$
    – dsollen
    Commented Mar 17, 2015 at 20:00
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    $\begingroup$ trying to keep it away from the government could be rather hard, that's for sure. I mean, password protection would be nearly impenetrable since they don't have a computer to attack the password, and would have to do it manually. Not to mention the fact that your programmer is the only one who 'speaks' the programming language(s) he uses. But it gets hard to protect if the government is willing to forcefully coerce him into cooperating. They can't kill him...but they could easily look for leverage on him. $\endgroup$ Commented Mar 17, 2015 at 20:03
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    $\begingroup$ I had imagine the protagonist being slightly paranoid of this risk, being afraid that a password can always be broken just by spying on you when typing etc. Thus he claims to have backdoor and other systems installed on the OS which will kick in if he doesn't regularly get free access to 'defuse' them. The truth is he doesn't know how to implement them and can't look it up, but they don't know. I think the government will mostly work with him, he is the one overly worried about them strong arming him, but it comes up when he tries to set terms to push more progressive policies $\endgroup$
    – dsollen
    Commented Mar 17, 2015 at 21:15
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    $\begingroup$ @guildsbounty, leverage could be a positive thing too. "What do we offer this guy to cooperate with us?" It is said that you catch more flies with honey than vinegar. $\endgroup$
    – Monty Wild
    Commented Mar 17, 2015 at 23:36
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    $\begingroup$ I just had way too much fun in Microsoft Calculator pretending to be a time traveller $\endgroup$ Commented Mar 18, 2015 at 1:59

Note to time travelers: Beware of unintended consequences! Here's one rather significant problem that might occur:

  • Modern cryptography enables the Allies to crush the Germans much more quickly. Suddenly, they have a lot more resources to devote to taking down Japan.
  • The Japanese Empire crumbles beneath the onslaught. There is no need to use the atomic bomb on them to force them to surrender.
  • The Manhattan Project was still there, though, and was probably helped along quite a bit by this computing technology. (See other answers to this question.) Now we have atomic bombs, but have never used them on Hiroshima and Nagasaki.
  • The USSR continues to rise. After a while, war breaks out in Korea. General McArthur wants to use the atomic bomb on the North Koreans and/or the Russians and/or the Chinese. (See: actual history.)
  • Because it never got used (very sparingly) to end a war, after which there was an interim period of a few decades during which we learned about the horrific after-effects of nuclear weapons, President Truman doesn't force him to resign over this, and The Bomb is now used (enthusiastically) at the start of the next war. Great horrors ensue.
  • $\begingroup$ >There is no need to use the atomic bomb on them to force them to surrender. There actually was no such a question whether to use the bomb or not. To quote Alex Wellerstein, the modern scientific consensus is the following: ''It was war; Truman had atomic bombs; it was taken for granted, at that point, that they were going to be used." blog.nuclearsecrecy.com/2013/03/08/… Also the Japanese primarily surrendered because of the Soviet invasion of Manchuria, althought the bomb was important too: it was a good excuse for the Japanese public. $\endgroup$
    – ain92
    Commented May 27, 2019 at 14:52

At the risk of offending some, I think several of the answers on this thread are overestimating the skills of the average, fresh out of school, programmer.

Being in the field, and having interviewed more recent graduates than I want to count in the past few years, I would estimate that somewhere over 80% of the people getting software degrees are doing so because they have heard there is high demand, and the money is good (both statements are true btw). The result is that many of them do not have the natural aptitude and personality traits that make one a good programmer. They got through school, and can be helpful in an established team with experienced people to coach them along, but they can't produce effectively if thrown out on their own with only vague directions from people that don't understand the code any better than they do.

If our time traveler is such a person, then the laptop is primarily going to be useful as a calculator. The programmer just doesn't have enough experience or understanding to do anything else effectively. At best the programmer will be able to implement the algorithms designed by the mathematicians of the era once they gain an understanding of the computer's strengths and weaknesses.

However, if the programmer falls into the group that does have some level of aptitude, then there are numerous possibilities. Stick them in a room with some theoretical scientist and they will be able to generate the algorithms that help to test their theories. Give them a dataset (and people to do the data entry for it), and they will be able to design a database and pattern analysis algorithms to predict future probabilities. Basic cypher algorithms are definitely possible without any deep knowledge of cryptography, but you need a computer on the other end to decrypt them if it is anything more complicated than you could already do by hand. Brute forcing existing cyphers and generating one time pads are probably among the most useful tasks they could do in the realm of cryptography. Creating drafting and 3D modeling tools would help speed the process developing useful prototypes.

The catch is that the average laptop is still relatively limited in terms of space and processing power. While several orders of magnitude greater than what was available at the time, it will only be able to do a finite number of things before you have to start getting rid of the old stuff to make room for new items. As someone else noted, the only functioning interfaces are the built in ones that people interact with directly (screen, keyboard, speakers, etc.). There is no way to batch information in or out of it, no printers, & no storage media. If you delete something it is gone. The laptop also becomes a single point of failure. If too much relies on what it can do then what happens when it crashes? Eventually something in there is going to fail, and there is no way to recover it.

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    $\begingroup$ I don't think you offend anyone. I just think that because this question appeared on the SE hot list, you have a biased audience. Most of us probably come at it from what we think we could do with it. And as it's a world building situation I would naturally assume that the OP would write it so that our programmer in question had some natural aptitude. $\endgroup$
    – Ryan
    Commented Mar 19, 2015 at 3:03
  • $\begingroup$ I think you make valid points, but at the same time having an incompetent programer as a protagonist would be rather unsatisfying. I imagine the programer as being intelligent and having a knack for programming, but still limited by limited 'real-world' experience. The key thing is he has the right programming mindset and CAN grow and develop. His weakness is he has a limited API and no resources to look up the what he hasn't memorized. Likewise he has the foundation to keep up with math/science well enough to translate a complex formula to code, even if he couldn't come up with it alone $\endgroup$
    – dsollen
    Commented Mar 19, 2015 at 14:42
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    $\begingroup$ @dsollen, haha yea. you asked a question about a time travailing programmer on a site connected to the most widely used programming site in the world :P $\endgroup$
    – Ryan
    Commented Mar 19, 2015 at 17:32
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    $\begingroup$ The time traveler doesn't need to be a particularly skilled programmer at all - they really only need to be able to explain some way of creating and running crude custom programs to the experts of that era. Input will be via a rotation of gentle typists entering batch jobs and intercepts submitted on paper, output will be photographs of the screen returned for interpretation. Sooner or later the keyboard will wear out, though a replacement for the electromechnical parts probably can be fabricated. Filtered cooling fans will be added... $\endgroup$ Commented Nov 19, 2017 at 21:29
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    $\begingroup$ @Ray How many fresh-out-of-school programmers have a copy of the language specification on their laptops? I mean, why bother when you can just access the internet anywhere and get more up-to-date info, better comments and stackexchange.com? $\endgroup$
    – user10328
    Commented Aug 4, 2018 at 16:05

Others have discussed code-breaking or code-making, which would certainly be useful, but my first thought was more direct:


One of the early projects in computing had a goal of pre-calculating shell trajectories to support targeting in the field. This is the ENIAC project. I expect a modern laptop could generate the firing tables needed by artillery operators in a fairly short period, giving our side a massive advantage in being able to target artillery quickly in the field. Even if our protagonist knows nothing but basic programming, he should be able to go to the mathematicians working on these tables and coordinate to crunch all the numbers at a speed that would seem like magic to them.

  • $\begingroup$ That is true, but in this scenario there is only one laptop that is non-replaceable. Is it feasible to call back to some central, WELL GUARDED, head quarters to generate firing solutions using a single shared computer? $\endgroup$
    – dsollen
    Commented Mar 17, 2015 at 17:38
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    $\begingroup$ @dsollen No, that's what artillery tables are for. $\endgroup$
    – Mike L.
    Commented Mar 17, 2015 at 17:42
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    $\begingroup$ As a side effect, having such a laptop would disrupt the investment and research in projects such as ENIAC, possibly slowing down the development of time-appropriate computers as any short-term feasible calculation problem can be handled faster on that single laptop as opposed to a single slow large system that might exist after a few years of building it. $\endgroup$
    – Peteris
    Commented Mar 17, 2015 at 22:30
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    $\begingroup$ Interesting. I could see ENIAC being cancelled, and similar effect on projects during the war. But after the war, I would expect a surge in computer research, possibly resulting in development faster than the original timeline. This would be a combination of two factors. First, seeing what computers will be capable of would push investment from people who otherwise would have seen computers are some esoteric academic thing at this point. Second, the laptop itself would potentially allow number crunching that wasn't available to engineers the first time around. $\endgroup$
    – Bryon
    Commented Mar 17, 2015 at 23:03
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    $\begingroup$ @BryonDowd: I don't think the Army would scrap all computing efforts in favor of a single artifact of unknown provenance and reliability. To the contrary, I would think a laptop might give overly-optimistic view of what investments in computing could achieve. The extent to which that might be a good or a bad thing would depend upon how well the programmer could help with the construction and use of computers using 1940s technology. Certainly in the history of computing a lot of effort has been wasted on efforts that didn't pan out, so knowing what things worked and didn't... $\endgroup$
    – supercat
    Commented Mar 18, 2015 at 23:42

Your every-man wouldn't have to do it all himself. I mean, if he had a interest in WW2 cryptography then he probably could do it all himself. Here's an enigma machine made with Javascript. Likewise, he could know German. But he doesn't need to do either of those things.

I think that a modern laptop in WW2 would be the most useful if you got it to the people who ended up breaking enigma. If you showed up at Bletchley Park and said "I have a computer and the knowledge of how to program it, help me with the math" You'd speed up the cracking speed exponentially, which would probably have shortened WW2 by a lot, having that knowledge earlier than they did.

Other effects

Breaking enigma is great, but he could also help develop better ciphers for the allies that would have stumped the Germans.

Having a little foreknowledge of WW2 events would have helped the allies too. To say "the Germans are going to go around the French Maginot Line though Belgium, attacking from the low countries and forests. Please warn them."
Without France surrendering Germany would have been weakened.

You wouldn't have even needed to know that much history. Just saying "yeah, that plan to assassinate Hitler in his bunker that you're working on, it fails. try something else."

With some science and physics background, he probably could help give a boost to a lot of the science with better gun design. Jet turbine theory, etc.
Even without knowing exactly how to do something, just giving the raw ideas would do a lot. "I see you are doing it that way. Have you ever though about switching it around?"
A lot of our ideas seem obvious, but they weren't until they were.

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    $\begingroup$ I was intentonally thinking of making the protagonist really ignorant in history just to prevent him from cheating too much with warning them of things. Besides, once you change the beginning of the war even a history experts advice would degrade as events transpired differently. Making him ignorant to these things avoids having to address how history changed and what knowledge was and wasn't still accurate. $\endgroup$
    – dsollen
    Commented Mar 17, 2015 at 17:17
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    $\begingroup$ According to wikipedia: German code breaking in World War II achieved some notable successes cracking British Naval ciphers until well into the fourth year of the War so having some better number crunching could be helpful. I definitely see the point of having him be ignorant, but with all the movies and stuff it's hard to be totally clueless, so some almost forgotten tidbit could slip through. Kind of like the bit about the Maginot line. I remembered my dad telling me about it 25 years ago (geeze) and I didn't remember it until I started typing this up... $\endgroup$
    – AndyD273
    Commented Mar 17, 2015 at 17:55
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    $\begingroup$ Of course, you wouldn't want literally to say "I have a computer", since they'd say "So do we, many of them"—the word having a different meaning to them. $\endgroup$
    – LSpice
    Commented Mar 17, 2015 at 20:28
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    $\begingroup$ As I've understood, the french were well aware that the effect of the maginot line was that the germans had to chose between going directly at it or through Belgium. What did surprise the french was that the germans chose to do their main armored assault through the dense Ardennes forest, this was considered a risky move, but it was carried out and the effect was that the french army and the BEF in Belgium got cut off. Had the allies been able to entrench and fight a regular battle in Belgium, they could have used their superiority in number of men And tanks to win (Dyle Plan.) $\endgroup$
    – Mårten
    Commented Mar 18, 2015 at 8:00
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    $\begingroup$ @dsollen Very good point. Probably wise idea you had just to avoid the issue. If anyone is wondering why he doesn't give some advice to help win the war, he could just say he doesn't make things worse with his crappy memory. In all honestly, that's probably what would happen to me... not wanting to look like an idiot to all these historical people, so just making some excuse like 'I can't tell you what will happen because history is already changing.' Which would also be true. $\endgroup$
    – AndyD273
    Commented Mar 18, 2015 at 15:53

User @Jorge Aldo said the biggest impact in a comment.

It's to the Manhattan project. You can read in this newspaper article from the 25th anniversary of the first nuclear reactor that Fermi wasn't very afraid of a uncontrolled nuclear reaction, but steps were taken against it. Well one of the reasons he wasn't afraid was because they spent several months before this event confirming the math! Boom laptop == months saved right there with some modeling.

On top of that you have the huge mathematical problem of building a machine (yes machine, not bomb) that will detonate. You can read a little more about that here but to summarize: To obtain critical mass and make sure it would detonate, in a machine small enough to be dropped from a plane, the boundaries of math, physics, engineering and chemistry were pushed to the absolute limits.

Oppenheimer and his team at Los Alamos, did massive amounts of theoretical work and put in crazy amounts of hours for years to push those boundaries. The computational power of a modern laptop in that environment would've been absolutely crazy. Seriously, single biggest impact would've been here, not code breaking, not telling people the future, but getting that laptop into the hands of the team assembled at Los Alamos.

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    $\begingroup$ Good luck convincing them to trust the city of Chicago to your unheard-of technology; unless you bring along engineers to explain exactly how and why this works, I don't see why they'd just trust you. $\endgroup$
    – cpast
    Commented Mar 18, 2015 at 5:07
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    $\begingroup$ @cpast As long as the machine is capable of producing high quality, verifiable calculations rapidly, I fail to see how the scientists will not trust it. Just make sure it isn't a Pentium V or you might get shot as an enemy spy. $\endgroup$
    – March Ho
    Commented Mar 18, 2015 at 6:28
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    $\begingroup$ Feynman wrote about his job doing calculations at Los Alamos. Blowing away that effort is something concrete you can write about, even making the real code and including it in the story with actual timing results and issues to overcome such as the built-in floating-point not having enough digits. $\endgroup$
    – JDługosz
    Commented Mar 18, 2015 at 8:57
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    $\begingroup$ and yet I shudder to think what would happen if I had an off-by-one error in my for loop for a model. Your programmer becomes a single point of failure, since no one else knows how to use the computer enough to verify he put the calculations in right. $\endgroup$
    – dsollen
    Commented Mar 18, 2015 at 14:59
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    $\begingroup$ @dsollen: Many of the computers in World War II (i.e. women who did computations) spent much of their time doing computations for hypothetical scenarios which didn't pan out. Given a list of input parameter values that would work, the World War II computers could have verified them as just as they, in reality, did with the actual parameter values that had been reached through trial and error. $\endgroup$
    – supercat
    Commented Mar 18, 2015 at 23:47

Many of your questions have already been answered in the Foresight War by Anthony Williams, written in 2004. In this 'alternative history', a military history expert armed with a laptop wakes up in London 1934. (At the same time, a modern German history expert wakes up in Berlin...) Very interesting idea and does show how quickly our past events would be altered if different actions had been taken.

Another good yarn is John Birmingham's Axis of Time Trilogy which involves a multinational naval task force being transported from 2021 to the Battle of Midway in 1942. That really is a world turned upside down with the sudden introduction of a huge array of advanced equipment and future knowledge.

Happy reading!

  • $\begingroup$ Nice reads (+1); I'll certainly try to find them. You might want to see this meta post, though, and see if you can tie these books even closer to the specifics of this question. $\endgroup$
    – HDE 226868
    Commented Mar 20, 2015 at 0:15

There's a few challenges here...

Laptop incompatibility. It's hard enough to get an apple to talk to a Microsoft machine as is, but in the end, your laptop is a complete stand alone machine. There is no wifi, no networking...there isn't even floppy disks. Every piece of information that makes it on to this computer is going to make it there by being manually typed in. This introduces a bit of a bottleneck...and it's very unlikely that an electronic English to German dictionary is going to be available if you don't already have it.

Second issue is getting anyone to believe you. If you started warning people that the Germans would attack France through Belgium and around the Maginot line, you would have joined a chorus of other voices that were saying the same. Charles de Gaulle referred to it as the Maginot mentality and had been fighting the dependency on it since the early 30's, including an expansion of defensive forces on the flanks (tanks, Charles de Gaulle was all about armoured warfare and a modern army). If they ignored someone such as Charles de Gaulle, do you really think they'd accept the warnings of an Englishman claiming to be a time traveller? Chamberlain was warned a multitude of times of Hitlers actions and the prospect of war, yet he consistently opted for a pacification diplomacy route until Churchill took power. There's no way American intelligence 100% missed Japans rise in the pacific and a potential attack. Stalin chose to believe Hitlers peace, despite intelligence to the contrary, until Hitler actually attacked. Having the knowledge is meaningless if nobody will listen to it.

And the third...war is hell. It's complete chaos. I was watching a history channel show that detailed the first tank only attack...which was completely accidental. The assault was supposed to include air support and infantry, but poor weather prevented this and the attack was called off. Nobody told the tankers and they left at the scheduled time...resulting in the first 'amoured blitz' of sorts. There is a friendly fire incident where an attack was called off so heavier bombardment could start...nobody told the Canadians and they went in during the heavy friendly fire bombardment. Even if you had the knowledge, you are depending on it to be used in a time where communication isn't assured.

If the person had some very specific and indepth history of world war II and was pre-trained for this, I could see a decent impact, especially in being able to 'forsee' some of the Germans tactics. A person going in with a little bit of processing power and programming skill...I don't really see it impacting that much for the allies.

Oddly enough, I see the time traveler going back to aid Hitler significantly more effective...but this is due to a few very bad intelligence failures on his part. Look up Pattons 'balloon army' and the impact that had on D-day as an example...or conscripting Ukrainians to fight the Russians instead of suppressing them.

  • $\begingroup$ I agree that the laptop is a stand alone machine. However, they already had people trained to type (on type writers). An average typer manages 40 Words per minute. a dictionary has ~171,000 words. so working around the clock a few typists could add a new dictionary in about 5 days (they have to type two words per dictionary, English and German, so twice as long then you may think). Of course in reality you would want a much shorter dictionary with only a list of common words to save memory, and someone else to sanity check 'close' results. $\endgroup$
    – dsollen
    Commented Mar 17, 2015 at 19:11
  • $\begingroup$ as for the rest, as I said the idea was to shy away from using historical knowledge to change the war, bcause it's so hard to emulate the butterfly effect, and because frankly that's not the interesting part of the story I want to tell. Thus the only thing my protagonist needs is to prove that his laptop works. a challenge to get the right people to look at it, but not impossible story to make happen. $\endgroup$
    – dsollen
    Commented Mar 17, 2015 at 19:14
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    $\begingroup$ And, some computer programs come pre-installed with multiple language packs. All the dictionary information is in there already, you'd just need to pull it out of that program's library and make it freely available. For code breaking, you don't need to know what german words map to which english words. You just need a list of all the german words...the Allies had plenty of linguists who could do the translation for you. And as for 'proving yourself' all you have to do is show someone the horsepower your laptop runs with. They'll take that seriously, at least. $\endgroup$ Commented Mar 17, 2015 at 19:14
  • $\begingroup$ @guildsbounty - You'd have to find more than just 'someone' to show it to and you'd need that someone to take it seriously and be influential. As Ville Niemi comments, the code was broken for a period before the war...but you need someone to take it seriously and act upon it, otherwise it doesn't really help anyone. Chamberlain was a pacifist dedicated to keep the peace through pacification...you could have shown the man detailed German plans of the invasion of Britain, but I find it quite doubtful that he'd believe you until after the invasion began. $\endgroup$
    – Twelfth
    Commented Mar 17, 2015 at 19:27
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    $\begingroup$ @Twelfth Right...which is why you go to the scientists, not the politicians. If you walked up to Oppenheimer and told him you had a way to do heavy calculations ten thousand times faster than they could currently be done...he'd probably hear you out from sheer curiosity. Then one demonstration later, you've made your point. $\endgroup$ Commented Mar 17, 2015 at 19:30

Some of it relies on what software you have on the machine.

Even a fresh install windows machine would change the face of that war as many of the other answers point out.

If you could also cram the disk with whatever software and technical info you wanted (manuals, source code and compilers for whatever software you wanted, design and manufacturing detail for chips, modeling software, books of algorithms, crypto software) you could probably change the whole 20th century and jump the whole field of computer science forward by decades.


First of I would teach all my knowledge to the most brilliant minds and logicians back then like Alan Turing, and I would write my knowledge down. You don't have to know everything about a programming language, it is enough if you understand the basics (e.g. control structures, functions, variables etc.) just teach them everything you know at the current time and show them many code examples and show them how the syntax works, maybe even let them write some simple codes by themselves so they understand the basics.

Also there is a chance that you will find some scripts from games, programs or the operating system. You can inspect and learn from them, there is a chance that you can learn something new just by reading these scripts, e.g. a new control structure (for, while, switch...). The more knowledge you can gather, the better.

At the end these brilliant minds will most likely be able to write own scripts and get much better in scripting, programming than you and can use and apply that knowledge thanks to your teaching.


To be a dissenting voice amongst all these answers, let me point out that Enigma was broken historically, and the effect of a modern laptop employed in codebreaking would have either no or negative effects for the side that used it.

One of the dilemmas of codebreakers is how much to rely upon the messages they decode. Do so too much, and the enemy will begin to suspect that their code has been broken. If that happens, it becomes likely that they will change their encryption. This is the dilemma that England faced with respect to Enigma, so breaking more German messages faster would actually not help.

If the British high command, presented with a "magical" codebreaking machine, became overconfident and overused its results, the result would be that the Germans would change their encryption. If that too became obvious that it had been broken, the Germans would raise the game yet again and again until the resultant cipher could not be broken by the magical laptop. This might even be something on the order of a codebook of abbreviations for common words and situations (for conciseness) run through a one-time-pad, which is unbreakable via cryptanalysis, and would require capture of the German pads in such a way that the Germans didn't know that they had been captured, otherwise the Germans would simply invalidate the captured pad series and issue new pads. End result: the Allies know even less than they did historically.

  • $\begingroup$ of course it needs time to distribute one-time-pads to all your units and submarines and you may not want to do it every week. $\endgroup$
    – Henning M.
    Commented Nov 20, 2017 at 23:50

Perhaps they would use it to run simulations of different strategies of how to win the war.

But I imagine, the laptop would be considered so precious and valuable that people would be incredibly scared to break it. If the laptop crashed it would be devastating. Imagine if the battery run out and people thought the laptop was dead. Someone would be found responsible and shot!

It might also be looked on with immense suspicion. People would distrust the results. And say it was trickery.

  • $\begingroup$ Welcome to the site :) $\endgroup$
    – dsollen
    Commented Sep 10, 2018 at 12:26
  • 1
    $\begingroup$ I doubt people would understand the potentiality of a laptop in the few hours it takes the battery to run low. $\endgroup$
    – L.Dutch
    Commented Sep 19, 2018 at 3:20

One of the beginners' schoolbook definitions of a computing process is something that makes input, processing, and output. It's the input and output that are huge pain in the behind, read on to find out why.

Russian Sci-Fi strikes back!

Although some books were already mentioned, there was this guy who landed in Russia with his truck full of computer appliances and a laptop. In 1965. And that was already hard enough.

The setup

The time traveler worked as a communications engineer, hence he has all the kind of connectors and adapters from USB to RS-232 and what not in his truck. Along with quite sizeable amount of technical literature on the pin-out and voltages of the connectors.

And even then it's horribly hard. Basically, the author was cheating a bit and cutting corners to make up for some unfortunate tech decisions in the USSR. Further, mostly important to change the course of the history was

  • the actual historical knowledge: there was a clash of two political groups in the party, you'd need to know this and to try to reach the right people;
  • time traveler's car. It was an old Japanese 4WD, old enough to be able to dismantle and understand it. Further, the "computer" topic leads to the injector controller based on local tech. Which is quite a feat for late 60s.


So, in early 70s we would have:

  • Political changes;
  • A significant boost to the computer industry in the USSR and world-wide, basically, a jump of 5-7 years ahead;
  • Some (immediately top-secreted) code breaks;
  • Tetris arcade machines world-wide;
  • Injector-based motors;
  • A snowboard (just 'cause it's a hobby of our time-traveler).

The impact

My point is: it was really hard for a time traveler to make a significant technical impact. The most important thing was the knowledge of the person themself.

A major plot of the novel series is the interaction of modern hardware with then-available interfaces. Hence the "inherited" USB-COM adapters, ancient network cards in the trunk, etc. Basically, without some hardware support (that would be unlikely possible to produce in then-time) and know-how (both human knowledge and software support), interfacing a modern machine with older tech is very very hard.

Yes, you can take pictures and even film the screen. But the use of a modern laptop as a number cruncher in the past while keeping the secrecy and using more than a single user for input, is rather hard. The next point is that modern hardware is not really made for a 400% workload torture over years. Part would break and at some point the laptop would be impossible to repair with then-tech.

The differences to the question

So, it was all quite hard and the author was cutting some minor corners to make it work. In 1965. With full government support, time traveler's own research institute for computing and so on. It would be much, much harder in 1940. You wouldn't even have RS-232 to interface with! (It's from 1960.)

In fact, any transistor tech before/during WW2 is a quite alien thing for then-locals. A power supply? Sure! An amplifier? Why not! Capturing the screen? Yeah! Doing the actual digital input/output? No way!

So, yeah, it would be for decades the world's most advances supercomputer, but rather limited to a single person who can work with it. Even having all programming books of the world available on the machine with some usable compilers and tool chain and world top scientists doing the "actual" programming on the paper, the bottle neck would be the input/output of code and data.

(In the novel the time traveler is resorted to brute forcing some cyphers in Excel(!), because he has no tools, does not know better, and cannot outsource. Remember: a comm eng, not a programmer! With a top-top secret assignment!)


For years I have had a list of things I would want to take with me if I was to travel back in time to the ethernet era.

  • One modern computer with a 100 mb ethernet interface (your laptop would work for this, although my list would use a rackmount server), running linux.
  • One twenty four port ethernet switch (I only need twenty one ports, but no one makes twenty one port switches, and twenty four port switches are common).
  • Twenty one ethernet cables.
  • Twenty 10base-t aui adapters.
  • one full set of software cds w/ source (I probably would use debian).

I would then locally source twenty computers with two ethernet cards to use as routers, terminal servers and terminals.

To update the list for your scenario, I would aim for the teletypes, because ethernet is not yet available. So drop the aui adapters, add terminal servers, modems, an oscilloscope, a frequency counter and the rs232 specifications. (I would use 33kbps modems because of their error correction, and that they would be all but impossible to eavesdrop on at the time, but I probably would run them at 300 baud so that they could be used with locally produced teletypes, which could be produced sooner with the test equipment and the rs232 and ascii specifications. the ascii specification just happens to already installed, not to mention I can recreate from memory the whole table in about twenty minutes.)


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