Pipes

This page explains how to lay pipes, how troop flow works through them, and why supply lines matter.

Laying pipes

Pipes connect a cell to an adjacent cell in one of four directions: north, east, south, or west. A cell can hold up to four directional pipes — one per direction.

Click near the edge of a selected cell (or press i/j/k/l) to toggle a pipe toward that edge.
Right-click or Alt+click (or Alt+i/j/k/l) lays an exclusive pipe: it replaces all other pipes in that cell with a single pipe toward the chosen edge.
Space clears all pipes in the selected cell.

See Controls for the full command tables.

How flow works

Every tick, each pipe delivers troops into the neighboring cell it points at. The delivery rate depends on the slope between the two cells (Δ = destination elevation − source elevation):

Slope	Flow per tick
Downhill (target lower)	8–12 troops — the steeper the drop, the faster the flow (Δ=1 → 8, Δ≥5 → 12)
Flat (equal elevation)	7 troops
Uphill (target higher)	6→1 troops — the steeper the climb, the slower the flow (Δ=1 → 6, Δ=6 → 1)
Steep uphill (Δ≥7)	0 — stalled

Flow never drains the source cell. Only the destination gains troops.

The uphill trap

Uphill pipes are the classic new-player trap. You can lay them, and they appear on the board, but every step of climb costs speed. Gentle uphill pipes still move troops — just slowly. Steep uphill pipes (a climb of 7 or more elevation steps) stall completely and move nothing. A stalled pipe renders as a hollow triangle on the board, so you can spot a dead supply line at a glance. When a push stalls for no apparent reason, check whether you asked troops to walk uphill.

Two more limits

Water stops flow: a pipe pointing into water delivers nothing.
Destination cells cap at 30 troops; a full cell accepts nothing until it has room.

Pipe slope colors and intensity

Each pipe triangle on the board is colored by its slope classification:

Slope	Color	Visual treatment
Downhill	Green	Filled triangle; size scales with gradient strength
Flat	Amber	Filled triangle; smallest size (no gradient signal)
Uphill	Red	Filled triangle; size scales with gradient strength
Stalled	Gray	Hollow (outline-only) triangle; fixed size

Intensity encodes gradient steepness as triangle size. Stronger slopes produce bigger triangles:

Downhill intensity: Δ=1 produces a small triangle; Δ≥5 (the maximum bonus) produces the largest.
Uphill intensity: Δ=1 produces a small triangle; Δ≥7 (stall point) produces the largest — but stalled pipes are always fixed size with the hollow treatment instead.
Flat pipes have the smallest triangles (no gradient signal).
At low zoom levels, a minimum triangle floor ensures pipes remain visible.

Feeding and decay

Troops cut off from supply do not wait politely — they die:

A stack (all the troops sitting in one cell) in an open cell with no incoming pipe flow loses 1 troop per tick to decay.
City cells never decay: their own production feeds them every tick.
Any friendly inflow counts as feeding, even a trickle — the minimum non-zero flow is 1 troop per tick, and it keeps a forward garrison alive.

Mutual feeding

Two cells piping into each other sustain each other indefinitely: each counts as fed by the other’s flow, so neither decays. This is the standard way to hold a stable front line — pipe your forward cells into each other and neither rots.

Reserves interact with decay too: reserved troops cannot be eaten by decay. See Reserves.

Pipes as tactics

Arteries: long chains of downhill/flat pipes stream fresh troops from safe cities toward the front.
Severing: paratroopers clear every pipe in the cell they land on — enemy supply lines are targets (see Special weapons).
Stalemates: two mutually-fed fronts can outlast anything thrown at them; breaking one usually means cutting the other’s feed with paratroopers or guns.

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