Snake in the Tunnel

The Snake in the Tunnel was a 1970s European currency arrangement that constrained the fluctuations of member currencies within a tight band (the “snake”) while the band itself could move within a wider corridor (the “tunnel”) against the US dollar. It represented an early attempt to insulate European economies from the volatility unleashed by the Bretton Woods system’s collapse.

The problem it solved

When the US abandoned fixed-rate gold convertibility in August 1971, the postwar anchor for world currencies vanished overnight. The dollar began floating; major currencies drifted and gyrated. For European nations tightly integrated in trade, this instability was intolerable. A 10% swing in the Deutsche Mark against the franc in a quarter made it impossible for manufacturers to plan cross-border investment or pricing.

European policymakers, led by the West German Bundesbank, sought a middle path: keep intra-European rates largely stable (to preserve trade predictability) whilst allowing some flexibility against the dollar. The result was the Snake, agreed in April 1972.

How it worked

Under the Snake, member currencies were allowed to fluctuate against each other by no more than 2.25% (later tightened). So if the Deutsche Mark’s parity was set at 1 DM = 2.50 French francs, the franc could trade in a band of roughly 2.44–2.56 francs per mark. Each pair had its own band. At the same time, the collective group’s average (the “tunnel”) could move by up to 4.5% against the dollar over the same period.

This created a multilateral commitment to stability: if one currency weakened too much against the others, central banks would intervene—buying the weak currency, selling the strong one—to pull it back within the band.

Which nations joined and why

The Snake began with six members: West Germany, France, Belgium, the Netherlands, Luxembourg, and Denmark. Over time, the roster proved unstable. The UK briefly joined but withdrew within weeks in June 1972, unwilling to subordinate sterling to Deutsche Mark discipline. Italy departed in 1973. Sweden, Norway, and Austria joined, then left. By the late 1970s, the group had shrunk to a core of Deutsche Mark devotees: Germany, the Netherlands, Belgium, and Luxembourg.

The defections reflected a harsh truth: the Snake worked only for countries willing to import German monetary policy. West Germany, as the strongest and most inflation-averse economy, set the tone. Countries running higher inflation or deeper recessions could not sustain the band—they either had to painfully deflate or abandon the peg.

Why France and Italy couldn’t stay

France, weakened by post-1973 oil shocks and higher inflation than Germany, found its franc slipping repeatedly toward the weak edge of the band. To hold the rate, the Banque de France would have had to raise interest rates sharply, choking off recovery during a recession. Politically untenable. Italy faced similar pressures with the lira. Both eventually exited, devalued, and built separate escape valves into their currencies.

The repeated crises—and exits—taught a hard lesson: a currency band works only if the central banks at the edges are willing to sacrifice domestic employment and growth to defend it. This constraint would resurface in the later Exchange Rate Mechanism.

The Snake’s limitations

The Snake was clever in theory but brittle in practice. It offered no institutional framework for deciding when a “realignment”—an agreed, coordinated devaluation of weak currencies against strong ones—was appropriate. Each time such a discussion arose, it became messy and humiliating: the weak-currency nation had to negotiate a concession while stronger partners extracted political or trade concessions in return.

Moreover, the narrow 2.25% bands meant that even small shocks—a surprise inflation reading, a shift in oil prices—could force intervention. Central banks drained reserves supporting their currencies and accumulated reserves when they overshot. The system became a constant tug-of-war.

There was also no supranational authority to manage the tunnel against the dollar. The Snake’s strength depended on US dollar movements, which the US did not control for the Snake’s benefit; the Fed pursued its own monetary policy. When the dollar weakened sharply in 1973–74, the entire tunnel shifted, and members had to adjust their external terms of trade. When it strengthened in the late 1970s, the reverse squeeze hit.

Legacy and lessons

The Snake is often dismissed as a failure, and by sheer participant count it was: most members quit. Yet it achieved two important things. First, it demonstrated that European monetary cooperation was possible and desirable—that the political benefits of a stable exchange-rate zone outweighed the loss of independent monetary policy. Second, it foreshadowed the institutional design of its successor, the Exchange Rate Mechanism, which added an explicit realignment mechanism and later became a stepping stone to the euro.

The Snake was the Continent’s first step toward monetary union. It failed, but it showed the way. Without the Snake’s pioneering—and its failures—there would have been no ERM, and possibly no euro.

See also