The week sterling stopped an army
In late October 1956 British and French troops landed in Egypt to retake the Suez Canal. Militarily the operation worked. Paratroopers took their objectives. The canal zone was within reach. Two of the most experienced armies on earth were executing a plan they had rehearsed for months.
Then the pound started to fall. Speculators attacked sterling and the Bank of England burned through foreign exchange reserves at a rate London could not sustain. Chancellor Harold Macmillan went to the International Monetary Fund for an emergency loan. Washington blocked it. The United States also refused Export-Import Bank credit and threatened to sell its own sterling holdings, a move that would have devalued the pound outright. The message from Eisenhower was simple. No ceasefire, no money.
Britain accepted a United Nations ceasefire on November 6, days into a successful operation. France followed. Prime Minister Anthony Eden resigned within three months. The National Army Museum's own summary of the lesson is blunt. From that point on, any major British operation would need American approval.
Nobody defeated the British army. The army depended on an economy, the economy depended on a currency, and the currency depended on a foreign government's goodwill. The dependence sat three layers below the soldiers and none of them could see it. Capability on loan is capability with conditions. Britain learned the terms in the worst week possible.