In November 2024, 5.2 million Swedish households opened their post and found a booklet telling them to be ready to cope on their own for at least seven days. No attack had been announced. No storm was on the forecast. Over the next two years the same kind of message went out from Helsinki, Brussels, The Hague, Warsaw, Berlin and London. Then, in September 2026, the Pentagon told America's biggest military bases to be able to run without the civilian grid at all.
Governments don't usually ask people to store water in peacetime. When so many do it at once, it's natural to assume they know something the rest of us don't. Sweden's civil protection agency had a plainer explanation: "The security situation is serious and we all need to strengthen our resilience to face various crises and ultimately war," its director, Mikael Frisell, said when the booklet went out.↗
That still doesn't explain the numbers. Why 72 hours in Brussels and seven days in Stockholm? Why does the US Army work to 14 days? And why, if the threat is war, was the most dramatic European blackout in two decades caused by something else entirely? The answers sit in three places: a run of real incidents, the physics of how a power grid falls over and gets back up, and some sober arithmetic about how long rescuers need to reach everyone.
What actually changed?
Start on Christmas Day 2024, at 12:26 Eastern European Time. Estlink 2, the main high-voltage cable carrying electricity between Finland and Estonia under the Gulf of Finland, failed. Cross-border capacity fell from 1,016 megawatts to 358. That evening four telecommunications cables in the same waters were reported disrupted, and two were completely severed. Finnish investigators suspect the oil tanker Eagle S dragged its anchor across the seabed along a track several tens of kilometres long. The anchor was recovered on 7 January 2025, and the power cable wasn't repaired until June.↗
Incidents like that are hard to prove and easy to repeat. You don't need a missile to cut a country's electricity link. A ship and an anchor will do, and the ship can sail away while lawyers argue about intent. Since Russia's full-scale invasion of Ukraine in 2022, European governments have filed this kind of sabotage, along with cyberattacks, drones and disinformation, under the label "hybrid" threats: damaging, deniable and below the threshold of open war.
Now the twist. The biggest grid failure Europe has seen in a generation wasn't sabotage at all.
At 12:33 Central European Summer Time on 28 April 2025, the power systems of continental Spain and Portugal went completely dark.↗ The expert panel convened by ENTSO-E, the body that coordinates Europe's grid operators, called it "the most serious event in the European power grid for over two decades." Its final report, published on 20 March 2026, found no attacker. It found voltage swings and oscillations that tripped generators offline, mostly solar and wind plants connected through inverters, followed by a cascade of overvoltage shutdowns until the Iberian system lost synchronisation with the rest of continental Europe. Portugal took about 12 hours to restore supply. Spain took about 16.↗
That's the real lesson governments took from the past two years. The cause of a long blackout matters less than its length. An anchor, a ransomware gang, a winter storm and a voltage oscillation all end in the same dark kitchen. Britain's new preparedness campaign was launched with storms, wildfires and conflict all on the list, alongside what Defence Secretary Wes Streeting called "increasingly sophisticated cyber attacks". He put the risk in a single shopping-trip question: "How would we cope if the payment systems at the local supermarket went down?"↗
- US Army installation energy and water policy sets a 14-day minimum.
- Sweden starts mailing about 5.2 million copies of If Crisis or War Comes: cope for at least seven days.
- Finland publishes its national guide: at least 72 hours.
- Estlink 2 power cable and four telecom cables damaged in the Gulf of Finland.
- EU Preparedness Union Strategy: 30 key actions, supplies for at least 72 hours.
- Iberian blackout. Spain and Portugal go dark at 12:33 CEST.
- Germany's civil protection office advises stocks for 10 days.
- Netherlands begins delivering a 72-hour guide to more than 8.5 million households.
- Poland begins mailing a safety handbook to all 17 million households.
- ENTSO-E final report on Iberia: a cascade, not an attack.
- Finland's "Shelter 2026" exercise in Kuopio simulates cyberattacks on power and water.
- Pentagon memo creates the FORTRESS America programme.
- UK launches "Be Ready": three days of food and water.
Figure 1 — Nine years of preparedness decisions, with the grid incidents in between. Blue marks military policy.
Why can't they just switch it back on?
Because a power grid isn't a set of wires. It's one enormous machine. Every large generator connected to Europe's continental grid spins in lockstep at 50 cycles a second, and every second the electricity going in has to match the electricity coming out. Too little supply and the frequency sags. Too much and it climbs. Voltage behaves in a similar way, and it varies from place to place.
Equipment on the grid is built to protect itself. When frequency or voltage strays outside safe limits, automatic relays disconnect generators and lines before they can be damaged. That's sensible for each machine and dangerous for the system: every plant that trips off shifts the burden onto the ones still running, which can push them past their own limits. In Iberia the trigger was overvoltage, and the cascade took the whole peninsula down in seconds.
Most power stations need electricity to start: pumps, fans and control systems all run on it. After a total blackout there's nothing to borrow. Operators begin with a small number of plants that can start themselves, such as hydro dams, diesel generators or large batteries. They use them to energise a few lines, bring bigger stations up one at a time, match each new island of supply to the same frequency, and only then reconnect customers, in blocks small enough that the sudden demand doesn't knock everything over again. It's slow on purpose.
How slow? Britain has written it into law. Under the Electricity System Restoration Standard, the national grid operator must have arrangements in place, by 31 December 2026, to restore 60% of regional demand within 24 hours and 100% of the country's electricity demand within five days.↗ Read that the other way round: the UK's own worst-case plan assumes some people are still without power on day four.
And electricity is the thing everything else leans on. Mobile phone masts need power, and most don't carry much backup. Ofcom found that only around 20% of UK mast sites have at least an hour of battery backup, and about 5% have six hours or more. It estimates that giving almost everyone up to four hours of access to emergency calls would cost about £1 billion.↗ Card terminals, petrol pumps, lifts, fridges and water treatment all depend on the same supply. Finland's September 2026 exercise in Kuopio started from exactly that chain: a simulated cyberattack that took out the city's power and its water together.↗
Why 72 hours, and why two weeks?
The European Union's answer came on 26 March 2025, when the Commission launched its Preparedness Union Strategy: 30 key actions and an action plan, built on a report by former Finnish president Sauli Niinistö which concluded that strengthening Europe's preparedness was "a matter of urgency." For ordinary people the headline was a single line encouraging them to keep "essential supplies for a minimum of 72 hours in emergencies."↗
Why three days? Finland's guide gives the clearest reason: "When people can cope for at least 72 hours on their own, the authorities can focus on their own tasks."↗ The logic is triage. If most households can look after themselves, ambulances, generators and water tankers can go first to hospitals, care homes and the people who can't.
Norway asks for more and explains why in three parts. Losing electricity, water, sewage, internet and mobile networks for longer than a week is rare. A week gives "you, your loved ones and the authorities some time to plan the way forward." And a week is "realistic to achieve for a large proportion of the population." Its storage target for water is 20 litres a person.↗ Sweden's booklet asks households to be "prepared to cope for at least seven days – ideally longer" and to plan for at least three litres of water per person per day.↗ Germany's federal civil protection office goes furthest of the large states, advising stocks for 10 days.↗
The longer recommendations come from countries that sit closest to Russia or have kept a Cold War habit of "total defence", where civilians are part of the plan. The 72-hour countries are mostly planning for the more likely emergency: a storm, a flood, a long outage. Neither group is wrong. They're planning for different emergencies.
| Country / body | How long | Launched | Reach |
|---|---|---|---|
| Sweden (MSB) | At least 7 days | 18 Nov 2024 | About 5.2 million booklets |
| Finland | At least 72 hours | 26 Nov 2024 | Online national guide |
| European Union | Minimum 72 hours | 26 Mar 2025 | Guidance to all member states |
| Norway (DSB) | One week, 20 L water per person | Current guidance | National campaign |
| Germany (BBK) | 10 days | Oct 2025 | Updated national guide |
| Netherlands | First 72 hours | 25 Nov 2025 | 8.5 million+ households |
| Poland | 3 days | Dec 2025 | 17 million households |
| United Kingdom | 3 days | 22 Oct 2026 | "Be Ready", year one of three |
The Pentagon's two weeks
The military number is older than any of the European ones, and it has a refreshingly practical origin. In February 2017 the US Army signed an installation energy and water security policy requiring its bases to be "capable of providing necessary energy and water for a minimum of 14 days." The Army said it arrived at two weeks by studying "past power outage and water shortage patterns" and matching them to what its critical missions needed.↗ In other words, 14 days was roughly how long the worst real outages had lasted, with a margin.
The 2026 push goes further. On 30 September at Marine Corps Base Quantico, Pentagon chief Pete Hegseth announced that major US installations would generate their own power, independent of the civilian grid. If an adversary takes down the grid, he said, "our bases stay lit."↗ A memo the same day ordered a FORTRESS America programme office to be stood up within 30 days. On 25 October, Fox News Digital reported internal documents setting a goal of at least 90 days of independent operation for major continental US bases. The Pentagon hasn't clearly confirmed that figure. Its chief spokesperson, Sean Parnell, told Fox: "Power is combat now."↗
The toolkit is microgrids (local networks that can disconnect from the public grid and run on their own generation), large batteries and small nuclear reactors. The Army's Janus programme aims to install more than 20 microreactors at bases starting in 2028. Those plans sit on top of older targets: a microgrid at every Army installation by 2035, and microgrids at 16 Air Force bases by fiscal 2030. The scenario the planners worry about most is a conflict with China that opens with cyber and physical attacks on US energy infrastructure, aimed at stopping forces before they leave home.↗
So the civilian and military numbers measure different things. A household's 72 hours or seven days is time to wait for help. A base's 14 or 90 days is time to keep working while there isn't any.
So should you be worried?
Mostly, no. The governments asking for this are going out of their way to say so. Britain wants people "alert but not alarmed," in Streeting's words.↗ And the base rate is reassuring: according to Ofgem data cited by Ofcom, about 90% of British power cuts last between three minutes and three hours. A winter storm is far more likely to test your cupboard than a war.
But "not alarmed" isn't the same as "nothing has changed." What has changed is the kind of risk. Grids are bigger, more interconnected and more digital than ever, which makes them efficient day to day and more exposed to a cascade, a cyberattack or an anchor in the wrong place. The Iberian report shows the system can fail without any enemy. The Baltic cables show an enemy wouldn't need much. Either way, the result is measured in hours and days, not minutes.
The good news is that the fix at household level is cheap and boring. Official lists overlap heavily: drinking water (somewhere between three litres a person a day and Norway's 20 litres a person in total), food that doesn't need a fridge or a stove, a battery or wind-up radio, a torch or candles, a first-aid kit, and a plan for how your family will find each other if phones go down.↗ In Britain, anyone who depends on powered medical equipment can join their energy and water companies' free Priority Services Register to get help first during an outage.↗
Back to the question from the beginning. Governments aren't preparing because they know a date. They're preparing because they worked out how long a bad outage lasts, compared it with how long most homes could cope, and found a gap. The US Army did the same sum in 2017 and landed on two weeks. Most homes, until very recently, had planned for zero.
That leaves a harder question for the rest of the decade. A household can fill a cupboard in an afternoon. A society that runs its money, water and phones on a single always-on grid has a much bigger cupboard to fill, and nobody has yet put a number on that one.
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