OpenFront Nukes — Cost, Blast Radius, SAM

An atom bomb costs 750,000 gold and a hydrogen bomb 5,000,000 gold. The first city costs 125,000 gold, so one atom bomb is six cities and one hydrogen bomb is forty.

Which gives you the answer most of the time: late, and only against someone you cannot out-grow. Gold spent on nukes early comes straight back as falling behind.

Prices

MIRV cost scales with how many you have already launched: 25,000,000, then 40,000,000, then 55,000,000.

Blast radius

The hydrogen bomb’s inner radius of 80 is far larger than the atom bomb’s outer radius of 30. It costs 6.7× more and destroys considerably more than 6.7× the area.

Troop casualties are computed from density (5 × troops ÷ tiles owned). A target with troops packed into a small area is worth far more per warhead. Against a sprawling empire, one atom bomb hurts much less than you would expect.

Silos and range

Nukes launch from the nearest silo and land where you clicked. Default targeting range is 150 tiles.

• Silo reload is 9 seconds, and levelling up does not shorten it
• A level-N silo fires N nukes back to back. Level buys you salvo size, not reload speed
• Construction takes 10 seconds. A slot added by upgrading starts cold and waits the full 9
• Silos are buildings, so they transfer with territory. Never build on the border

A silo site has to satisfy two conditions at once:

1. Targets within 150 tiles
2. Outside enemy SAM range

SAM — what it stops and what it does not

SAM range grows with level:

range = 150 − 480 ÷ (level + 5)

It approaches 150 asymptotically and never exceeds it. Level 5 is the point where it finally covers a hydrogen bomb’s 100-tile blast.

There is no level cap. You can keep upgrading as long as you can pay, but range only creeps toward 150 — what levels actually buy is simultaneous intercepts.

Reload, precisely

A SAM holds one loaded slot per level, and each slot returns 9 seconds after that slot fired — the building does not go dark for 9 seconds.

So upgrading never costs you current coverage. Upgrading after you see an inbound nuke loses nothing — it just will not help against that one.

The MIRV misconception

“SAMs cannot stop MIRVs” is the usual shorthand. More precisely:

SAM targets are atom bombs, hydrogen bombs, and MIRV warheads. Warheads are on the list. What is not on the list is the MIRV carrier before it splits.

There are three reasons they get through, and volume is the last of them.

1. Speed. A MIRV warhead moves at 22; a SAM interceptor at 12. It cannot catch up
2. No shot on the final step. Interception is only evaluated up to the second-to-last point of the trajectory. Anything already on your doorstep is untouchable
3. Volume. The warheads arrive together and reload is 9 seconds

So it is not “cannot intercept” — it is “fast, caught late, and numerous.” Levelling up eases (3) but does nothing about (1) or (2). Several SAMs will stop part of a salvo, but blanketing your territory in SAMs to counter a 25,000,000 attack is rarely the better trade.

A SAM under construction does nothing at all

SAM construction takes 30 seconds, and during those 30 seconds its interception ability is not partial — it is exactly zero. The interception logic is only attached once construction completes.

• Progress bar at 90% → zero intercepts
• There is no threshold like “once the gauge is part-filled.” It is complete or it is nothing
• For those 30 seconds the structure is simply a target that a nuke deletes

Starting one because you see an inbound missile never works. Build it the moment a neighbor acquires a silo.

This is not a SAM quirk. Every structure under construction has zero function. A city being built does not raise your cap; a defense post being built does not defend the border. Factories are the one case that leaks the wrong way — an unfinished factory already counts toward the dispatch denominator, so until it completes it only lowers your other factories’ odds. At 2 seconds the real cost is tiny, but it is the only place in the game where the under-construction state does harm. → Factory and Rail Income

What a nuke aims at

When a nation bot picks a target it scores every structure in the blast and sums them. Scores scale with level.

Your silo is worth double a city as a target. And because level multiplies, one level-4 city (100,000) is a juicier target than two level-1 silos.

Two modifiers sit on top:

• Distance from the bot’s own silo is penalised (distance × 30, never below 20% of the structure value). Nation bots therefore hit whatever of yours is nearest to them — which is why your outlying buildings get hit before your core
• On Medium, everything within 50 tiles of one of your SAMs is off the table. Those tiles are scored −1 and dropped from consideration entirely

A SAM itself is worth zero as a target. Bots do not aim at your SAM; it dies because it happened to sit inside the blast aimed at the city next to it. The exception is Impossible + hydrogen bomb: only then do level-4-and-below SAMs that can be outranged pick up 100,000 per level, which makes them the top priority.

Spacing — the real threshold is 200 tiles

“Spread your buildings out or one nuke takes them all” is common advice. The question is how far.

Minimum structure spacing is 15 tiles, so the most buildings that can physically sit inside a blast is:

163 buildings fit inside a hydrogen blast even at maximum spacing. “Spread out so a hydrogen cannot cover you” is not an achievable instruction — for most empires, every building you own is inside one blast.

The threshold that does mean something is this:

To keep two clusters out of a single hydrogen bomb, they need more than 200 tiles between them. The radius is 100, so the diameter is 200.

On the M grid:

Against atom bombs (radius 30) it is far easier — 60 tiles, about half a cell on World, separates two clusters. Early and mid game that is the only version worth planning around.

🟢 Structures inside the kill radius always die. No roll, no partial damage, no level tanking a hit. And the check does not care who owns them — a strike near your own border deletes your buildings and your allies’ too. Land tiles get a probabilistic reprieve in the outer band; structures get none.

So when?

Gold priority is almost always: three cities → ports and factories → defense posts → (much later) silos and nukes. Reasoning in How Many Cities Should You Build?.

Two side effects

• Fallout persists and adds a defense multiplier to those tiles. Nuking land you intend to take works against you
• Using a nuke can break alliances. Be careful firing near allied territory

Accepting an alliance deletes nukes already in flight

The moment an alliance request is accepted, every nuke travelling between those two players is cancelled. For a MIRV, cancelling the carrier takes its already-released warheads with it.

That cuts both ways.

• Under fire — if you see a nuke inbound, sending an alliance request or accepting one you already have is the only live counter. No SAM required
• Firing — if the target has an alliance request pending with you, resolve it before you launch. A 5,000,000-gold hydrogen bomb evaporates on a single click of “accept”

Launching is briefly blocked right after an acceptance, so “get them to accept, then fire” does not work either.

More

• Building cost calculator — silo and SAM totals
• All Six Buildings — silo and SAM placement
• How Many Cities Should You Build? — the opportunity cost